Comparative Morphology, Anatomy, Phenology and Reproductive ...

Aust. J. Bot., 1990, 38, 523-41

Comparative Morphology, Anatomy, Phenology and Reproductive Biology of Alexgeorgea spp. (Restionaceae) from South-western Western Australia

K. A . ~ e nA, eJ. ~S. pate

and K. W. ~ i x o An

* ~ i n g Park s and Botanic Garden, West Perth, W.A. 6005, Australia. B ~ e p a r t m e nof t Botany, University of Western Australia, Nedlands, W.A. 6009, Australia.

Abstract Morphological features of Alexgeorgea nitens, A . subterranea and a recently named new species, A . ganopoda, are described. All are markedly rhizomatous and clonal, with spaced aerial culms and sand-binding roots. A . ganopoda develops nodal and internodal apogeotropic roots. Male plants bear spikelets aerially, female plants sessile underground inflorescences at a maximum intensity of one flower per season's rhizome segment. Fruiting is geocarpic and seeds are extremely large for Restionaceae, e.g. 605 mg dry weight per seed in A . ganopoda, 190 in A . nitens, 162 in A . subterranea. Germination occurs while fruits are still attached to rhizomes. Germination is hypogeal, remotive in A . nitens and A . subterranea, admotive in A . ganopoda. Graminoid seedling leaves are formed in A . nitens and A . subterranea but not in A . ganopoda. Anatomy of culm, root and rhizome conforms generally to that of other Restionaceae. Xeromorphic features are exhibited by the two dry habitat species A. nitens and A . subterranea. Roots, rhizomes and culm bases of A . ganopoda carry interconnected cortical investments of aerenchyma, apparently as an adaptation to seasonally waterlogged habitats. Species-specific anatomical differences include the tissue architecture of culms, vascular bundle numbers in rhizome internodes and seedling leaf anatomy. Starch reserves are prominent throughout A . nitens, less so in A . subterranea and absent from A . ganopoda. Seed dry matter contains 57-59% starch. Male and female A . subterranea and male A . nitens reproduce annually. Female A . nitens flower very occasionally, mostly without setting seed. One known population of A . ganopoda is male and female fertile, the other almost entirely sterile. A . subterranea flowers in spring coincident with peak vegetative growth, A. nitens in autumn before the season's onset of growth. The reproductive phenology of A . ganopoda is unclear. The large-seededness, geocarpy and in situ germination of Alexgeorgea spp. represent an unusual form of clone replacement, resulting in establishment of seedlings within the wake of the advancing parent clone. The implications of this system are discussed.

Introduction

Alexgeorgea, a highly unusual large-seeded geocarpic genus of Restionaceae, was first described by Carlquist (1976), who named and provided morphological descriptions of two species, A . arenicola Carlquist and A . subterranea Carlquist from the Jurien Bay-Badgingarra region of the northern sandplains of south-western Australia. The former species was subsequently renamed A . nitens (Nees) Johnson & Briggs by Johnson and Briggs (1986), who confirmed its conspecificity with material initially named Restio nitens Nees. Recently, a third species, A. ganopoda Johnson & Briggs, has been recognised (Briggs etal. 1990) based on examination of unidentified herbarium specimens and recently collected material.

K. A. Meney et al.

All three species are strongly clonal and can be prominent or even dominant monocotyledonous components of the native floras of certain sandplain ecosystems. One of the species (A. nitens) is the subject of a recent study (Meney et al. 1990) on growth and resource partitioning, while this comparative study describes certain aspects of the morphology, gross anatomy and reproductive biology of all species and relates this information to the taxonomy, habitat preferences and pronounced clonality of members of the genus. Special emphasis is placed on the recently named species A. ganopoda.

Materials and Methods Study Sites and Plant Material The two more widespread and abundant species (A. nitens (KD877) and A . subterranea (KD878)) were subjected to routine monthly harvests of ramets at study sites at Eneabba (29" 49'S., 115" 16'E.) and Badgingarra (30" 25' S., 115" 30' E.) respectively during 1988 and 1989 in order to follow the seasonality of ramet growth and development and provide material for morphological and anatomical descriptions. The population of A. subterranea proved to be fully fertile in both its male and female clones. Exhaustive examination of a large number of unburnt and recently burnt populations of A . nitens showed the vast majority to be female sterile, but a few were able to produce the occasional female flowers, all of which failed to set fruit. However, a single sparsely fruiting population was discovered in a newly burnt site at Cataby (30' 44' S., 115" 32' E.), and this provided limited information on the reproductive biology of female plants of the species. The phenology of growth and reproduction of the new species A . ganopoda (KD879) was assessed (1989 and 1990) at study sites in unburnt, seasonally inundated sandplain at Mt Frankland (35" 53'S., 116" 48'E.) and at a recently burnt roadside population at Bow River (34' 58'S., 116" 57'E.). The population at Mt Frankland was predominantly both male and female sterile, although some plants were bearing seed at one disturbed roadside verge and the occasional male inflorescence was apparent elsewhere in the site. By contrast, male and female plants of the population at the Bow River site were reproducing prolifically at the time of examination (March 1990). These plants provided the bulk of the material on which the species description is based. Species authorities and nomenclature follow those given in Green (1985). Vouchers cited are housed at Kings Park and Botanic Garden.

Anatomy The anatomy of culms, rhizomes, roots, seedling leaves and seeds of each species was examined by light micrography of thin (1-4 mm) sections of glycol methacrylate-embedded material. Techniques of fixation and embedding were as described by O'Brien and McCully (1981). Sections were treated with periodic acid-Schiffs (PAS) reagent to locate starch reserves and counterstained with toluidine blue (pH 4.6) for cytoplasmic features. At least three separate specimens, each from a separate clone, were examined for each organ of a species. Comparisons of organ anatomy were based primarily on low magnification whole transverse sections of an organ, supplemented in certain instances by high magnification detail of specific tissues. A special study was made of the vasculature of photosynthetic branchlets of culms, roots and rhizomes to determine whether mean bundle numbers within these parts were species specific. This involved transverse hand sectioning of randomly selected material from at least 10 clones of a species.

Starch Reserves This analysis was based on harvests of 20-30 ramets carefully excavated from 5-10 separate clones of the two common species. A . nitens (female sterile clones, January 1990) and A , subterranea (female fertile clones, March 1990), and 10 randomly selected ramets from the extensive sterile population of A. ganopoda at Mt Frankland (March 1990). Each ramet was divided into age classes of component parts (root, rhizome, culm and fruits (if present)), including all living material up to 3 years of age (see Meney etal. 1990 for classification of ramet parts). Samples of seed of all species were also collected. Starch concentrations in dry matter of ramet parts and seeds were measured as described by Meney et al. 1990.

Comparative Morphology of Alexgeorgea spp.

Results Distribution Distribution ranges of the three species can be deduced partly from locations of identified herbarium material (all three species), data provided by Carlquist (1976), Keighery and Marchant (1979) (A. nitens and A. subterranea) and our own observations on all three species (Fig. 1). A. nitens extends widely from coastal sandplain southwards from approximately 40 km north of Eneabba into the understorey of Allocasuarina/ Banksia woodlands from Gingin (31" 2l1S., 115" 54'E.) to Margaret River (35" 57'S., 115" 04' E.) and eastwards to Pingelly (32" 33' S., 117" 05' E.), while A. subterranea is apparently restricted to low heathlands of the kwongan from Cataby to north of Badgingarra (Fig. 1). A. ganopoda is currently known from two restricted locations only, namely as a single large (2 km2) population primarily in seasonally inundated swamps but also extending into the fringes of adjacent open jarrah (E. marginata) forest in the vicinity of Mt Frankland, and as a roadside relic population on cleared sandplain at Bow River (Fig. 1). The three species are predominantly psammophilous but A. subterranea and A. ganopoda occasionally extend onto thin layers of sand over laterite. All appear to flourish most prolifically in disturbed habitats.

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Western Australia

Fig. 1. Distribution of Alexgeorgea ganopoda, A . nitens and A. subterranea in Western Australia.

Morphological Features Plant habit of all species is clonal, comprising long, creeping rhizomes and short aerially branched culms (Figs 2A, 3B, 40). Clones are normally dioecious with the male flowers borne above ground on culms (Figs 2B, 3A, 4A), the female flowers geophyllous on the rhizome (Figs 2C, 3B, 4B). Ramets of a clone can remain physically interconnected in A. subterranea and A. nitens for more than 20 years, but living rhizome connections can usually be traced back from a specific apex of a ramet for no more than 5 years. Ramets of A. ganopoda comprise only 4-5 years worth of living parts and connections with the parent clone withering and decaying within 6-7 years.

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Fig. 2. Morphological features of Alexgeorgea nitens. A , portion of ramet of sterile, presumed female clone. Approximate position of ground level is marked by a dotted line. 1C and 2C, first and second year culms; 1R and 2R, first and second year sets of nodal, sandbinding roots; NRh, lRh, 2Rh, new season's, first year and second year extensions to r h i ~ o m e of ramet. Scale = 1Ocm. B, upper photosynthetic part of culm of male reproductive clone showing male spikelets (MS) terminating culm branchlets. Scale = 2 cm. C , portion of female reproductive ramet with subterranean female inflorescence (FI) terminating a rhizome extension. St, withered stigma. Ground level is marked by a dotted line. Scale = 5 cm. D, terminal part of recently burnt female ramet. Note terminally located fruit (F), seedling-type, grass-like leaves (L) and new culms (NC) formed after fire. Scale = 5 cm. E, portion of female ramet with an associated 6-month-old seedling that has established in situ following germination of the seed of a fruit borne in an internodal position of the parent rhizome (Rh). Note seedling leaves (L), primary culm (PC) and sand-binding seminal roots (SR) on the seedling. The shoot of the seedling is 7 cm high.


Culms of A . nitens and A . subterranea are approximately 10-20 cm in length, those of A . ganopoda 2-4 times this length. Each set of culm branches of the first two species is subtended by a thin, highly lignified bare stalk (Figs 2 and 3) while culm stalks of A . ganopoda are thicker, less fibrous and covered by brown scale leaves (cataphylls) (Fig. 4). Usually only one culm is produced per rhizome each year, although several may ultimately be present at the same node due to new culms arising from old culm nodes in subsequent years (e.g. in A . nitens in undisturbed habitats). A. ganopoda may produce secondary branches on its older culms. Reduced non-photosynthetic scale leaves occur at nodes along the upper parts of the culms of all three species. The fully subterranean rhizomes of Alexgeorgea spp. are located at 10-15 cm depth. Each rhizome internode is partiy encased in giabrous scaie ieaves which usuaiiy persist for 4-5 years. Rhizome width (minus leaf scales) is 3-5 mm in A . ganopoda, 2-3 mm in A. nitens and 1-1 a5 mm in A . subterranea. Outgrowth of scale leaves precedes extension of the apical meristem of the rhizome by approximately 5-10 mm, thereby protecting the apex from damage or desiccation as it grows through the soil. Vegetative extension of A. nitens in open or disturbed habitats averages 16.4 2 0 - 8 cm each year but may occasionally exceed 40 cm, especially when the species is colonising bare areas of ground (e.g. fire breaks). Rhizome extension of A . subterranea averages 1.7 cm but may exceed 80 cm, that of A. ganopoda 19.8 7.2 cm. All species 23.0 frequently produce two or three shorter axillary rhizome branches each season concurrently with extension of the main rhizome. Vegetative spread is considerably reduced in heavily shaded habitats or where clones have become intermingled. A . ganopoda exhibits a highly distinctive root dimorphy in possessing both deeply penetrating geotropic tap roots (in excess of 1 m) (Fig. 4D and E), and finer apogeotropic roots produced both at the nodes and along the internodes of a rhizome (Fig. 4E). By contrast, all roots of A. nitens and A. subterranea are geotropic and produced only at nodes subtending culms. From one to three and occasionally up to six roots are borne at each node. Root length normally lies within the range 20-30 cm but may extend to 1 m in deeper sands. Roots of all species are strongly sand-binding and the resulting sand sheaths are usually of a width equal to or exceeding the diameter of the root. All three species produce extremely large fruits ( A . nitens 190 mg dwt per fruit, A. subterranea 162 mg, A. ganopoda 640 mg) consisting of a basally attached embryo, starchy endosperm and persistent pericarp. Fruits are subterranean (10-20 cm) and usually are produced mid-way along the rhizome, and rarely less than 5 cm away from the proximate culm. Seeds of all three species germinate in situ, as first described for A . subterranea by Carlquist (1976). Germination of A. nitens and A . subterranea is remotive (see Langkamp 1987) and hypogeal (Figs 2E, 3C), commencing with elongation of the cotyledon. The broken cap of the testa is retained at the tip of the cotyledon and appears above the soil surface approximately 2 weeks after germination (Fig. 3C). The plumule, at first partly encased in the cotyledon, gives rise to a number (3-5) of true seedling leaves (Figs 2E, 3C and E ) before forming the primary culm of the seedling (PC, Figs 2E, 3C). Each seedling initiates a pair of diametrically opposed rhizome extensions within the first growing season (Fig. 3F), although further extension of these does not occur until the following autumn when the primary culm is fully extended and the seedling leaves have senesced. New culms (NC, Fig. 3F) have usually formed within a year after germination. [Note: Seedling type, grass-like leaves also form on adult plants of A . nitens in response to fire or disturbance during road construction or maintenance (see Fig. 2 0 and E.)] A. ganopoda differs from the other species in demonstrating admotive (see Langkamp 1987), hypogeal germination, with the testa remaining below ground (Fig. 4C). Seedling leaves are not formed in this species, the primary culm (PC, Fig. 4C) arising directly following emergence of the plumule.

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Fig. 3. Morphological features of adult reproductive and seedling plants of Alexgeorgea subterranea. A , upper photosynthetic portion of culm of male reproductive ramet showing male spikelets (MS) terminating photosynthetic branchlets (PB) of the culm. L, scale leaves. Scale = 1 cm. B, portion of ramet of female reproducing clone showing recently withered sessile female inflorescence (FI) borne below ground on a 1-year-old rhizome extension (1Rh). lC, one year culm; ZC, two year culm; NRh, current season's rhizome extension. Approximate position of the soil is indicated by a dotted line. Scale = 5 cm. C , sequence of stages in germination and seedling establishment. 1, mature fruit attached to parent rhizome; 2, surface view of detached seed; 3, early stage of germination; 4, later stage in germination showing remotive mode of germination in which pericarp (P) is elevated above soil surface


Anatomical Features (Figs 5-7) The three species differ amongst each other in a number of features relating to the gross anatomy of their culms, rhizomes, seedling leaves and roots. Several of these features are of taxonomic value and appear to be related to habitat preferences of the species. Culm branchlet anatomy Despite differences in size and shape, the photosynthetic branchlets of culms of the species show the same basic, radially symmetrical construction when viewed in median transverse section (Fig. 5A-C). Each branchlet displays (a) a well defined epidermis lacking ch!oropkisis except in the guard ceiis iianking stomata, jbj a multilayered hypodermal zone of photosynthetic tissue, (c) an outer medullar ring of small peripheral vascular bundles and (d) a central, usually solid medullar region comprised of large scattered medullary vascular bundles within a ground tissue of large parenchyma cells. Major differences among the species are as follows: (1) More pronounced cutinisation of the epidermis in A. nitens (Fig. 5A) and A, subterranea (Fig. 5B) than in A. ganopoda (Fig. 5C). (2) Deeply sunken stomata in A. nitens, but not in the other species. (3) Minor peripheral vascular bundles and their sclerenchymatous sheaths bridging the photosynthetic tissue of A. ganopoda, minor vascular bundles well inside this tissue in the other species. (4) A multilayered sheath of sclerenchyma surrounding the medulla of A. ganopoda, but less prominent and lignified in the other species. (5) Stored starch in ground tissue of the medulla of A. nitens, and to a lesser extent in photosynthetic tissue of this species (Fig. 5G), but negligible starch reserves in the other species. (6) Two-layered chlorenchyma zone in A, ganopoda, 3-4-layered in the other species. (7) Pronounced partitions of lignified tissue [the so called pillar cells described by Cutler (1964)l dividing the chlorenchyma zone radially in A. subterranea (Fig. 5B and H ) but less prominently in A. nitens (Fig. 5A and G). Pillar cells absent in culm branchlets (as illustrated) but present in principal branchlets of culms of A. ganopoda. (8) Inwardly projecting extensions to the epidermal cells flanking the sunken stomata of A. nitens [Fig. 5G and see also description of the synonymous taxon Restio nitens by Cutler (1969)l and A. subterranea (Fig. 5H). Examination of a random sample of mature branchlets from a range (10-15) of ramets of clones of each species showed no significant differences among species in number of minor or major bundles per branchlet transection. Rhizome internodal anatomy Transverse sections of rhizome internodes (Fig. 5D-F) showed a clearly defined cortex consisting of an outer layer of thin-walled tissue and an inner ring of sclerenchyma. on the elongating cotyledon (C); 5,2-month-old seedling showing development of seminal system of sand-binding roots (SR) and presence of a number of grass-like seedling leaves (SL); 6, approximately 6-month-old seedling with well developed primary culm (PC) (Note: germination and seedling establishment normally occur in situ, in immediate proximity to the original female inflorescence. All seedlings shown were removed from parent ramets before photography.) Scale = 5 mm. E, 4-month-old seedling showing typical close proximity to parent ramet following in situ germination within a fruit formed on the internode of the rhizome. Note presence of seminal roots (SR) on the seedling, and nodal adventitious roots (NR) on the parent rhizome. SL, seedling leaves; PC, primary culm. Scale = 5 mm. F, IS-month-old seedling showing diametrically opposed rhizome extensions (Rhl, Rhz) each bearing a culm (NCI, NC2) and a further new season's rhizome extension (NRhl, NRh2). Remains of seedling leaves (SL) are present and the primary culm (PC) is still green and presumably active in photosynthesis. Scale = 5 cm.

Fig. 4. Morphological features of adult reproductive and seedling plants of Alexgeorgea ganopoda. A, male reproductive culms showing, from left, (1) branched culm with male spikelets (inflorescences) on most branchlets; (2) culm with both vegetative and reproductive branches; (3) fully reproductive culm. Scale = 5 cm. Inset below gives detail of male spikelets (MS). Scale = 1 cm. B, female reproductive ramet being intercalary subterranean inflorescences (Fl) on current season's extensions of main (MRh) and lateral (LRh) rhizome extensions. Dotted line designates ground level. Scale = 5 cm. Inserts show to left a young fruit (F) with withered remains of style (St) and in trio to right a mature seed (Se) with pericarp removed, and basal (F) and side (Fl) views of a complete fruit. Insets scales = 1 cm. C, young seedlings showing admotive germination with testa (T) remaining below ground. Note absence of grass-like seedling leaves (cf. A. nitens and A. subterranea) and direct formation of primary culm (PC) from the plumule. SL, scale leaves. Scale = 1 cm. D, second season seedling. Remains of endosperm (E) are attached, the primary culm (PC) is still green and two opposed rhizome extensions (Rhl, Rhz) carry culms and further extensions of their rhizomes. Note geotropic tap roots (TR) and series of internodal and nodal apogeotropic roots (AR). Scale = 5 cm. E, Terminal part of rhizome showing arrangement of internodal apogeotropic roots (AR), young primary tap roots (TR), new culm (NC) and new (NRh) and previous season's (1Rh) extension of rhizome. Scale = 1 cm.


The latter layer has been termed the endodermoid sheath by Cutler (1969). This sheath embraces a medullar region containing a number of collateral vascular bundles embedded in ground tissue. Differences among species include the following: (1) Loss of outer cortex from older rhizomes of A . nitens and A. subterranea (inset Fig. 5E). (2) Transformation of the outer cortex of A. ganopoda into a persistent layer of aerenchyma. (3) Heavier sclerification of the inner cortex in A. nitens and A. subterranea than in A . ganopoda. (4) Sckrifieb iiiiervasciiiar tissue in the meduila of A. subterranea, meduiiar starch in A. nitens, unspecialised medullar parenchyma lacking starch in A. ganopoda. (5) Starch stored in large quantity in all age groups of rhizomes of A. nitens, lesser amounts in A. subterranea rhizomes, and absence of starch in rhizomes of A. ganopoda. (6) Species-specific numbers of vascular bundles in rhizome internodes, i.e. 111 2 5.6 in A . ganopoda, 37 0.9 in A. nitens and 20 ? 0.5 in A. subterranea (all means significantly different, P I0.001).

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Basal culm anatomy Stalks of culms sectioned at or close to ground level (Fig. 6A-C) show very intense cortical and medullar sclerification in A . nitens and A. subterranea. In A. ganopoda, sclerification is minimal and the outer cortex is developed into an aerenchymatous layer similar to that found in the rhizome. Seed endosperm anatomy All species exhibit an essentially similar endosperm structure (e.g. see A . ganopoda, Fig. 6D), with a typical monocotyledonous outer aleurone layer containing protein bodies enclosing a starchy inner endosperm. Seedling leaf anatomy The grass-like laminae of seedling leaves of A. nitens and A . subterranea (Fig. 6E and F) show dorsiventral symmetry and linearly arranged vascular bundles located centrally within a photosynthetic mesophyll. Seedling leaves of A. nitens exhibit abaxial and marginal zones of sclerenchyma, adaxial groups of bulliform cells, and mesophyll concentrically arranged around the vascular tissue (Fig. 6E). Seedling leaves of A. subterranea display emergent stomata on both their upper and lower epidermal layers. As mentioned previously, seedling leaves are absent in A , ganopoda. Root anatomy Transverse sections of roots (Fig. 7) display typical monocotyledonous features, namely a polyarch xylem, large late developing metaxylem vessels and a strongly sclerified, single-layered tertiary-thickened endodermis. Mature roots of A. nitens and A . subterranea bear sheaths of sand grains trapped between long persistent root hairs. These sheaths and underlying epidermal and outer cortical tissues continue to invest the root long after death of all tissue outside the endodermis [e.g. see older roots of A. nitens (Fig. 7 B ) and A. subterranea (Fig. 7131. The broad cortex of the young tap roots and apogeotropic roots of A. ganopoda is made up of highly distinctive, symmetrically oriented radial files of cells (Fig. 7 0 ) . Death of these cells is followed by fragmentation or dissolution of tangential walls, resulting in a radially organised aerenchymatous layer (Fig. 7E-G) of essentially similar construction to that described above for rhizomes and lower parts of the culm. This layer and the bounding epidermis persist throughout the life of the root. Starch reserves are sparse, if present at all in roots of the species. Numbers of protoxylem groups visible in root transverse sections vary greatly within a species depending on size and order of roots. Mean bundle numbers were found not to differ significantly among species.

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Fig. 5. Anatomical features of culms and rhizomes of Alexgeorgea spp. A and G, T.S. of culm photosynthetic branchlets of A . nitens. Note starch reserves (S) in ground tissue of medulla, heavily catinised epidermis (E), sunken stomata (ST) and inwardly projecting extensions of the epidermal cells flanking the substomatal cavity (arrow in G). Pillars (P) of non-photosynthetic tissue almost bisect the bays of chlorenchyma (C). B a n d H , T.S. culm branchlets of A . subterranea. Stomata (arrow in H)are not sunken, substomatal cavities are lined by inner margins of the epidermal cells (5 H ) and pillars of sclerenchyma (asterisk) partition the bays of chlorenchyma (C). C , T.S. culm branchlet of A . ganopoda. Note that the ring of minor vascular bundles (MB) is located within rather than inside the

comparative Morphology of Alexgeorgea spp.

Starch Content of Vegetative Parts and Seed Analysis of ramet parts and seeds of the three species confirmed the above anatomical evidence of substantial differences among species and organ types in ability to store starch. Starch was present in significant amounts (1.4-4.4% of dry matter) in culms and rhizomes of A. nitens (see also Meney et al. 1990) and in somewhat lower amounts (1 -7-2.7%) in roots of this species. Culms of A. subterranea varied in starch content (0-4.2%) depending on age of culm, as also did rhizomes (0-2.5%), while roots of this species were devoid of starch. A. ganopoda did not contain starch in vegetative parts, except for low amounts in young culms (0.3%). Seeds of all three species were rich in starch (57-59% of seed dry weight). Phenology of Vegetative Growth and Seasonality and Frequency of Reproduction Seasonal vegetative growth of A. nitens and A. subterranea commenced in May-June. Extension of culms and most of the season's complement of new roots preceded that of rhizomes by 3-4 weeks. Production of laterals occurred within 3 weeks after root initiation, and a second crop of new laterals was observed to form in both species on roots up to 2 years old in response to unseasonal rain during February-March of 1989. Most roots had senesced by the end of their third year of growth, by which time they had lost their sand-binding capacity. Remains of dead roots were still present, however, on segments of ramets up to 10 years old. New roots of both species were 3-15 cm long by the end of September of the season of their initiation and had become heavily lignified by the end of October. Culms of A. nitens and A. subterranea were fully extended by the end of spring. A. ganopoda resumed growth immediately after onset of autumn rains in March 1990, i.e. earlier than the other species. In other respects its phenology of vegetative growth was similar to that of the other species. Culm longevity in the three species did hot normally extend beyond 2 years, and peak vegetative growth occurred in spring and early summer (e.g. see Meney et al. (1990) for A. nitens). Reproductive phenology differed among species. Flowering of A. nitens occurred in autumn (March-May), i.e. out of phase with vegetative growth, while that of A. subterranea took place in spring (September). Stigmas senesced within 2 weeks of emergence at the soil surface. Dead remains of male inflorescences remained attached to their parent culms for several months after shedding of pollen. Flowering in A. ganopoda was not observed but, based on the finding of developing fruits in March, it was suggested to be a spring-flowering species. The reproductive phenophases of A. subterranea, the species most intensively studied, were as illustrated in Fig. 8. Each seed took 12 months to mature after flowering chlorenchymatous zone (C), thereby forming girder-like partitions within the chlorenchyma. D, T.S. internode of young rhizome of A. nitens still enveloped by overlapping scale leaves (SL). Inner cortex (arrow) is already heavily sclerified but starch reserves are not yet laid down in ground tissue of medulla (M). E, T.S. internode of young rhizome of A. subterranea. SL enveloping scale leaves. Note thin-walled outer cortex (C) surrounding heavily sclerified central part of rhizome (M). F, T.S. internode of mature rhizome of A. ganopoda. A persistent aerenchymatous cortex envelops the central cylinder in which the vascular tissues are located. The inner cortex exhibits heaviest sclerification. G and H, high power views of outer region of photosynthetic culms of A. nitens and A . subterranea respectively. Photographs from sections shown in A and B respectively (captions given under A and B). I, high power view of T.S. of part of old rhizome of A. nitens. Note multilayered sclerenchyma (F) surrounding vascular core in which dense deposits of starch (arrows) are located. J, high power view of part of old rhizome of A. subterranea. Vascular bundles are completely enveloped in sclerenchyma. Scales: A-C, E and F = 0.2 mm. High magnification micrographs G-J at 6 x greater magnification than their respective counterparts at low magnification.

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Fig. 6 . Anatomical features of lower regions of stalks of culms ( A - C ) , a seed (D) and seedling leaves ( E and F) of Alexgeorgea spp. Culm stalks are heavily sclerified (F) in A . nitens ( A )and A . subterranea (B) but invested with an aerenchymatous cortex (AC) in A. ganopoda (C). Note restriction of stored starch (arrows) to the central part of the culm of A . nitens, and absence of starch in other species. Mature seed of A . ganopoda (D) shows distinct aleurone (A) filled with protein bodies (PB) outside the starch endosperm (SE). Seedling leaves of A . nitens ( E )exhibit hypodermal sclerenchyma (F),mesophyll (ME) arranged concentrically around the vascular bundles, bulliform cells (B) and sunken stomates (arrows).Seedling leaves of A . subterranea show dorsiventral arrangement of mesophyll (ME),emergent stomata (arrows) with well developed substomatal spaces, and lack hypodermal sclerification. Scales: A = O . l m m ; B = 0 . 2 m m ; C = 0 . 5 m m ; D = 20pm; E = l m m ; F = l m m .

Fig. 7. Anatomical features of roots of Alexgeorgea spp. A, T.S. of young root of A. nitens showing prominent endodermis (E) parenchymatous cortex (C) and stele with immature, late developing metaxylem elements (arrows). Scale = 50 pm. B, T.S. of one year root of A . nitens. Note collapsed dead cells of cortex (C) to exterior of heavily lignified endodermis (E), and presence of mature metaxylem vessels (arrows) in the stele. Scale = 100 pm. C, T.S. of old root of A. subterranea showing death of cortex (C), thickened endodermis (E) and pronounced ring of large metaxylem vessels (X) well inside the protoxylem groups (arrows). Scale = 0.1 mm. D, T.S. young apogeotropic root of A. ganopoda. Vascular tissues of stele (S) are mostly undifferentiated, but the highly regular cellular arrangement of the aerenchymatous layer of the cortex (AC) is already apparent. Note the sclerenchymatous hypodermis (H) inside the epidermis. Most of the root hair zone and its mantle of sand particles were removed prior to embedding and sectioning. Scale = 0.25 mm. E, T.S. mature tap root of A. ganopoda showing radial arrangement of air spaces (A) in cortex due to cell death and fragmentation of tangential walls. Note extensive medulla (M) in stele and large number of metaxylem elements. Scale = 0.5 mm. F, low power surface view of tap root of A. ganopoda showing relative widths of stele (pale central part labelled S) and aerenchymatous cortex (darker outer layers) labelled A. The root shown is 5 mm in diameter. G , high power view of part of section shown in E to give details of endodermis (E), xylem and air spaces (A) of cortex. X, metaxylem vessel. Magnification 6x that of E.

K. A. Meney et al.

but did not germinate in situ for a further 10 months (Fig. 8C). Thus, in January-June, a young developing fruit and a mature fruit were likely to be encountered on 1st and 2nd year rhizome internodes respectively (lRh, 2Rh, Fig. 8A). By July-August the older of these fruits was likely to have germinated (Fig. 8B), while by the following September-December a 3-year-old segment of a female ramet would carry a seedling,

5f

Jan

- April

July- Aug

.L

#

qd

S e ~t Dec

Fig. 8. Reproductive phenophases of a typical ramet of a female clone of Alexgeorgea subterranea which has engaged in reproduction in each of three successive seasons. NRh, 1Rh and 2Rh, new, first and second year rhizomes; NC, lC, 2C, new, first and second year culms; FL, flower; YF, young fruit; MAE, middleaged fruit; ME, mature fruit ready to germinate; S, seedling formed following in situ germination within a fruit still attached to the parent rhizome.

mature fruit and a new flower (Fig. 8 0 , provided of course that it had reproduced in each consecutive season. Pollination of all species was assumed to be anemophilous. Germination of seeds of A. subterranea was shown to occur in the first winter after a seed had entered its germinative mode, and was thus coincident with the physiological


senescence of the rhizome on which the seed was situated (see Fig. 8). Removal of mature seeds (10-11, 13 and 19 months old) and reburial (in August, November and May respectively) in habitat soil at normal rhizome depth did not induce earlier germination response than in still-attached fruits, although similar seeds germinated successfully (48%) in laboratory tests. Immature seeds (less than 11 months old) failed to germinate if removed and reburied in habitat soil. Seeds of A. ganopoda germinated in March-April, and had almost fully extended their primary culms (PC, Fig. 4C) within a month. By contrast, A . nitens and A . subterranea did not germinate until June-July and seedling culm extension awaited onset of higher temperatures in September. A. subterranea proved to be unique in respect of its high frequency of female floweriiig aiid seed production (Fig. 2 2 and E j . ir normaiiy produced one iiower per year per new rhizome segment, the latter being 5 months old at the time of flowering (see Fig. 8 and Carlquist 1976). Occasionally two flowers were produced coincidentally on the same rhizome segment and flowering on axillary rhizome branches was also observed. An anomalous pattern of flowering was observed in one clone of A . subterranea at Badgingarra (July 1989) in which occasional female flowers were found to be borne aerially on emerging new culms (see Fig. 30). All seven such flowers aborted but their parent culms matured normally. Sexually reproductive female plants of A . nitens were located only in occasional clones after fire or mechanical disturbance, although male clones flowered annually throughout the geographical range of the species. Extensive searching of a wide range of geographically distinct localities of A . nitens between Perth and Eneabba during March 1989 resulted in the discovery of nine female flowering clones at a site 1 km from Eneabba. Five of these clones were monoecious, a phenomenon previously unrecorded for this genus, although the male flowers in question failed to mature and produce pollen. Female flowers were recorded at two other locations, 30 km north of Eneabba and 50 km east of Eneabba. Flower numbers were low (less than four) in all but one clone, the exception being at the Eneabba minesite where 23 flowers were recorded on one clone. Of 35 flowers monitored, only one matured to early endosperm stage; all others had aborted within 3 months after stigma emergence. Mature seeds, and the first ever recorded seedlings of A. nitens, were found at one locality at Cataby during 1989 in an area of natural bushland which had been burnt on 9 March 1989. A total of 110 seedlings was located in three apparently separate clones after careful survey of a 1 km2 transect within the burns. No seedlings were found in similar surveys undertaken in adjacent unburnt areas. Excavation of ramets within these reproducing clones showed that a few still viable seeds had not germinated. The female-fertile clones of A. ganopoda at Bow River showed a high incidence of seed production. Germination of seeds was particularly pronounced in patches of the site where parent culms had been completely destroyed by fire. At a disturbed area of the Mt Frankland site large numbers of ungerminated viable seeds were found still attached to dead rhizome segments presumed to be 3 or 4 years old.

Discussion Species of the genus Alexgeorgea exhibit a number of vegetative and reproductive features which set them apart from most, if not all other members of the Restionaceae. Notable among these are a widely spreading clonal habit with very long inter-culm rhizome extensions, a geophilous flowering habit, extreme large-seededness, and in situ germination of seeds at depth within fruits still attached to the parent rhizome. Otherwise, however, the three currently known species of the genus exhibit typical restiad features in respect of both their anatomy and morphology. The genus may be regarded as xeromorphic (see Cutler 1972) in producing heavily lignified branched culms, nonphotosynthetic scale leaves and deeply buried creeping rhizomes. As with numerous

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other dry habitat species of the sandplains of south-western Australia (see Pate et al. 1984), Alexgeorgea roots are sand-binding and their extensive rhizosheaths may be regarded as a mechanism for protecting roots from desiccation during summer. Anatomical features of culms, rhizomes and roots of Alexgeorgea spp. conform generally to those already described for other genera of Restionaceae by Cutler (1969). Cutler (1972) places particular emphasis on basic culm anatomy in relation to the possible course of evolution within the family. He pictures the 'simple' or 'primitive' culm architecture as exhibiting a single-layered epidermis with paracytic stomata, a onelayered palisade of chlorenchyma, a complete cylinder or sheath of parenchymatous cells immediately inside the palisade, a cylinder of sclerenchymatous tissues in which an outer peripheral ring of small vascular bundles and an inner scattered grouping of larger vascular bundles are included, and a central parenchymatous pith which may break down to form a central cavity. Several further anatomical patterns (Cutler 1972) are regarded to have evolved from this basic pattern before or after separation of the members of the family between the Australian. African and South American continents. and as general responses to deteriorating, increasingly arid environments. Prominent amongst the advanced features are the presence of sunken stomata, protective cells lining substomatal cavities, and the presence of pillar cells or sclerenchymatous grinders extending radially through the chlorenchymatous zone from epidermis to the cortical cylinder of sclerenchyma. On this basis, the culm anatomy of Alexgeorgea spp. would show relatively advanced features, notably (1) a multilayered chlorenchymatous zone in all three species, (2) sunken stomata in A. nitens, (3) protective cells in A. nitens, (4) pillar cells in A. nitens, A. subterranea and in certain parts of the culm of A. ganopoda, and (4) sclerenchymatous girders enclosing peripheral vascular bundles traversing the chlorenchyma in A. ganopoda. Xeromorphic adaptations are best displayed in A. nitens, least in A. ganopoda - an observation fully consistent with the habitat preferences of the species. In addition to the above, several other types of anatomical differences are recorded among the three species of Alexgeorgea, and these together permit ready identifications between the taxa on purely anatomical grounds. Most noticeable is the much heavier sclerification of culm stalks of A. nitens and A. subterranea than A. ganopoda, the presence of starch in the first two but not the last species-specific differences in mean number of vascular bundles in transverse sections of rhizome internodes. and the mesence in A. ganopoda of an extensive fully integrated system of cortical aerenchyma throughout roots, rhizomes and lower regions of culms. The aerenchymatous investments to all underground vegetative parts of A. ganopoda, combined with the presence of prolific sets of nodal and internodal apogeotropic roots, would suggest specialisation towards seasonally flooded habitats. The efficacy of this aerenchymatous system is well demonstrated if one excavates a complete plant of A. ganopoda, submerges it fully in water and injects air via a syringe into the cortical aerenchyma of root, rhizome or lower culm. Escape of air through cut or broken surfaces is then observed at distances up to 15 cm from the point of injection, in some instances involving a clear transfer between gas spaces of root, culm and rhizome on adjacent regions of a ramet. Other members of the Restionaceae possessing apogeotropic roots are the New Zealand species Empodisma minus (Hook) Johnson & Cutler (ex Hypolaena laterzyora) (Campbell 1964) and the south-western Australian species Empodisma gracillimum (B. G. Briggs, personal communication). A close counterpart to A. ganopoda in terms of the above specialisations is found in the woody leguminous shrub Viminaria juncea, which by virtue of its aerenchyma and pneumatophore system is capable of rapid growth and nitrogen fixation when roots and lower stems are submerged in water (Walker et al. 1983; Walker and Pate 1986). The presence of distinct graminoid leaves in seedlings and recently burnt plants, as observed here in A. nitens and A. subterranea, is somewhat uncommon among


Restionaceae but has also been observed in seedlings of the genus Lepyrodia (B. G. Briggs, personal communication), Ecdeiocolea monostachya and Loxocarya spp. Morphologically similar juvenile leaves are also commonly encountered in seedlings and heavily grazed or burnt adult plants of a number of other monocotyledonous southwestern Australian sandplain species sympatric with A . nitens and A . subterranea, including Thysanotus asper (Liliaceae), Arnocrinum preissii (Liliaceae) and Caustis dioica (Cyperaceae). Possession of seedling leaves in Alexgeorgea spp. may be viewed as a mechanism for rapid onset and rate of photosynthesis in early seedling development, although it does not appear to result in noticeably more rapid overall rates of seedling growth in these species than in sympatric Restionaceae germinating at the same t h e [e.g. Restto afT. sphme!,-t~;s, Ecdeiocolca monostackya, LcpidoboPm chaetocephalus, L. preissianus, Lyginia barbata (Meney, unpublished data)]. Moreover, seedlings of A . ganopoda which lack seedling leaves appear to grow as rapidly as those of A . nitens and A . subterranea, although this may be partly due to the more than three times larger seed size of the former species. Fruits are excessively large in Alexgeorgea in comparison with other Restionaceae, e.g. 16-66 times the mass of the largest known seed in other species of the family (Restio sp. nov.) (KD 880) and 45-200 times the mean fresh weight of seeds of most other southwestern Australian restiads (Meney, unpublished data). As with most monocotyledonous species, the seeds of Alexgeorgea are rich in endosperm starch (57-59% of seed dry weight) which, when compounded with large seed size, implies a high cost to the parent plant in seed filling, traded against the provision of unusually great energy reserves for seedling establishment. However, low fecundity, expressed as only one seed at most per annual rhizome extension, appears to be counteracted by relatively high seed viability, as indicated by ex situ germination rates of 50% in Alexgeorgea spp. compared with mostly less than 2 % in other south-western Australian restiads (Meney, unpublished data). The phenology of A . subterranea differs radically from that of A . nitens, despite their closely similar vegetative morphologies and habitat preferences. A . subterranea exhibits synanthy, i.e. flowering concurrent with peak vegetative growth in spring, whereas A . nitens is strictly heterantherous, i.e. flowering in autumn but recording maximum vegetative growth in spring and early summer (see Meney et al. 1990). This difference has obvious implications in terms of seasonal resource deployment to seed filling, and it is likely that the sizeable starch reserves of culms and rhizomes of A . nitens may well be called upon during flowering, as well as acting as long-term emergency reserves for regrowth following fire or other non-seasonal stress agencies. The reproductive phenology of A . ganopoda is not fully clear at this stage, but vegetative growth of the species appears to occur predominantly in autumn and winter. The highly unusual geocarpic habit and in situ seed germination of Alexgeorgea spp. has been viewed by Carlquist (1976) as reflecting the ultimate in inefficiency in seed dispersal. Indeed, long distance dispersal might be envisaged only through the agency of landslide, erosion or possible dispersal by animal agencies. The likelihood of such events is slight and, as we have observed, surface or near-surface (up to 5 cm depth) germination of seeds under field or laboratory tests usually results in desiccation and death of seedlings. The protracted seed maturation period of evident for Alexgeorgea spp. is by no means unusual among restiads of Western Australia, several of which require periods of up to 12-15 months before their aerially borne seeds are ripe and dehisce (Meney and Dixon 1988; K. Meney unpublished data). However, the retention of seed at depth (10-15 cm) below ground and the timing of in situ germination to coincide with death of the segment of the ramet on which the seed is borne are apparently unique features for Restionaceae, and represent a highly novel mechanism of sexually consummated replacement of clones. The spacing of seeds along the rhizomes and timing of germi-

K. A. Meney et al.

nation are likely to ensure that new seedlings establish as widely spaced individuals, well within the wake of the radial spread of the parent clone, thereby minimising both parent : sibling and sibling : sibling competition. At the same time, the likelihood of both male and female clones arising among the progeny will ensure close proximity of male and female individuals for effective pollination during reproduction of the species. In addition to the above system of progressive clone replacement, the presence of aged, still viable seed within totally dead parts of clones of all species, and the discovery of isolated seedlings of A. ganopoda in disturbed areas several years after demise of the presumed parent clones, suggests a capacity for long-delayed re-establishment of the species after most or all of a population has been destroyed by fire or habitat destruction L U. . J l I. u. l. ltal l m other agencies. ii wouid be pariicuiariy interesting ro examine in greater detail the frequency and location of germination and seedling establishment events, and thereby evaluate fully the interaction of vegetative and sexually induced reproduction on long-term structure and demography of clones.

Acknowledgments We thank Paul Sanford for carrying out the analyses for starch, Joanne Dumaresq for assistance with photography and preparation of figures, and Bob Dixon for his consistent help and support. The authors gratefully acknowledge receipt of grants from Minerals and Energy Research Institute of Western Australia (MERIWA), AMC Mineral Sands, Alcoa of Australia (K.W.D and J.S.P) and Australian Research Council (J.S.P). References Briggs, B. G., Johnson, L. A. S., and Krauss, S. L. (1990). The species of Alexgeorgea, a Western Australian genus of the Restionaceae. Australian Systematic Botany 3, 751-8. Campbell, E. 0. (1964). The restiad peat bogs at Motumaobo and Moanatuatua. Transactions of the Royal Society of New Zealand 2, 221-4. Carlquist, S. (1976). Alexgeorgea, a bizarre new genus of Restionaceae from Western Australia. Australian Journal of Botany 24, 281-95. Cutler, D. F. (1964). Three cell types occurring in the cortex of the culm of various species of Restionaceae. Notes JodreN Laboratories 1, 11-13. Cutler, D. F. (1969). 'Anatomy of the Monocotyledons. IV. Juncales.' (Clarendon Press: Oxford.) Cutler, D. F. (1972). Vicarious species of Restionaceae in Africa, Australia and South America. In 'Taxonomy, Phytogeography and Evolution'. (Ed. D. H. Valentine.) pp. 78-83. (Academic Press: London.) Green, J. W. (1985). 'Census of the Vascular Plants of Western Australia.' (Department of Agriculture: Perth, W.A.) Johnson, L. A. S., and Briggs, B. G. (1986). Alexgeorgea nitens, a new combination in Restionaceae. Telopea 2, 781-2. Keighery, G. J., and Marchant, N. G. (1979). Notes on the biology and phytogeography of Western Australian plants. Part A: Restionaceae. Research Notes, Kings Park and Botanic Garden, Perth, W.A. Langkamp, P . J. (1987). 'Germination of Australian Native Plant Seed.' (Inkata Press Pty Ltd: Melbourne.) Meney, K. A., Pate, J. S., and Dixon, K. W. (1990). Phenology of growth and resource deployment in Alexgeorgea nitens (Restionaceae), a clonal species from south-western Western Australia. Australian Journal of Botany 38, 543-57. O'Brien, T. P., and McCully, M. E. (1981). 'The Study of Plant Structure: Principles and Selected Methods.' (Termarcarphi: Melbourne.) Pate, J. S., Dixon, K. W., and Orshan, G. (1984). Growth and life form characteristics of kwongan species. In 'Kwongan - Plant Life of the Sandplain'. (Eds J. S. Pate and J. S. Beard.) pp. 84-100. (University of Western Australia Press: Nedlands.)


Walker, B., and Pate, J. S. (1986). Morphological variation between seedling progenies of Viminaria juncea (Schrad. & Wendl.) Hoffmans (Fabaceae) and its physiological significance. Australian Journal of Plant Physiology 13, 305-19. Walker, B., Pate, J. S., and Kuo, J. (1983). Nitrogen fixation by nodulated roots of Viminaria juncea (Schrad. & Wendl.) Hoffmans (Fabaceae) when submerged in water. Australian Journal of Plant Physiology 10, 409-21.

Manuscript received 12 June 1990, accepted 8 August 1990