ISSN 00963925, Moscow University Biological Sciences Bulletin, 2011, Vol. 66, No. 2, pp. 51–52. © Allerton Press, Inc., 2011. Published in Russian in Vestnik Moskovskogo Universiteta. Biologiya, 2011, No. 2, pp. 7–9.
Floral Morphogenesis in Choripetalous and Sympetalous Members of Ericaceae s.l. (Ericales)1 N. A. Vislobokov Moscow State University, Biological faculty, Department of Higher Plants, Moscow, Russia email:
[email protected] Received May 24, 2010
Abstract—Choripetaly of Rhododendron tomentosum is the result of secondary reduction. Our data support earlier observations of P. Leins [4] that a rudimentary corolla tube occurs during early stages of floral devel opment. Choripetaly of Empetrum may be a plesiomorphic condition, because no vestiges of corolla tube were detected throughout all stages of flower development. However, a complete loss of corolla tube cannot be excluded. The type of congenital petal fusion varies within a group of closely related taxa of Ericaceae: Phyl lodoce caerulea has late sympetaly while Loiseleuria procumbens has early sympetaly. In contrast, in euas terids, the type of sympetaly appears to characterize taxa of higher rank. Key words: Ericaceae, choripetaly, early sympetaly DOI: 10.3103/S009639251102012X
congenital fusion, free parts of structures appear first, followed by their united portion. In the case of early congenital fusion, the united portion appears first, while free parts form later [6]. The type of congenital petal fusion marks (with some exclusions) two clades of euasterids. Each of these major clades contains sev eral orders [3]. The order Ericales belongs to basal asterids. The type of sympetaly has not been discussed in detail in previous published descriptions of floral morphogenesis in Ericaceae [4, 5].
Flowers with double perianth are typical for the majority of eudicots. One of key features of asterids is the occurrence of sympetalous corolla. However, not all asterids possess the corolla tube. Choripetalous members do not form a compact taxonomic unit within asterids. Consequently, corolla evolution in asterids was rich in homoplasies. These may be result of parallelisms and/or reversions. The family Eri caceae is interesting for that matter. Sympetaly is com mon in Ericaceae, but it is not manifested in some members of the family. For example, in tribe Empe treae, the corolla is choripetalous, and a member of the tribe Rhodoreae, Ledum palustre L. has corolla, which looks like choripetalous in anthetic flowers. This species is closely related to species of the genus Rhododendron (which have a wellpronounced corolla tube). In the modern literature, Ledum palustre is con sidered as Rhododendron tomentosum (Stokes) Har maja [1]. A study of flower development using ana tomical sections revealed occurrence of a short corolla during early stages of morphogenesis, which supports the hypothesis on the secondary nature of choripetaly in anthetic flowers of this species [4]. Sympetaly of most asterids (including Ericaceae) has a congenital nature, and direct fusion of initially separate petal margins cannot be observed during morphogenesis. Corolla tube appears as ab initio united structure. Two types of incomplete congenital fusion can be recognized, namely late congenital fusion and early congenital fusion. In the case of late
MATERIAL AND METHODS We studied flower morphogenesis in two choripeta lous (Empetrum hermaphroditum Hagerup and Rh. tomentosum) and two sympetalous (Loiseleuria procumbens (L.) Desv. and Phyllodoce caerulea (L.) Bab.) members of the family Ericaceae, which belong to subfamily Ericoideae in the classification based on molecular phylogenetic data [2]. Perianth and andro ecium are trimerous in E. hermaphroditum and pen tamerous in other investigated species. Empetrum her maphroditum and L. procumbens have one whorl of sta mens, while P. caerulea and Rh. tomentosum have two whorls. Gynoecium consists of six to nine carpels in E. hermaphroditum, of five carpels in Rh. tomentosum and P. caerulea and of two or three carpels in L. proc umbens. All samples were fixed in 70% ethanol. The material was dissected by tweezers and needles under stereomicroscope MBS10. Prepared material was transferred to 100% acetone via 80 and 96% ethanol, a mixture of ethanol (96%) and acetone (100%) in pro portion of 1:1 and two times in acetone (100%) (30–
1 The article was translated by the author.
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60 min for each stage). The material was then critical point dried in HITACHI HCP2 critical point drier using liquid carbon dioxide. Dried samples were mounted onto the stubs using double sided sticky tape or nail polish, coated with platinum and palladium using Giko IB3 ion coater and observed using a Cam Scan S2 scanning electron microscope (SEM). The obtained images were saved digitally. RESULTS AND DISCUSSION The calyx of Rh. tomentosum appears as a mer istematic ring, which has five distinguishable apices of sepals. The sepals of P. caerulea and L. procumbens appear as distinct primordia in a helical sequence. The sepals of E. hermaphroditum also appear as distinct pri mordia, but simultaneously. Junctions appear between the petals of Rh. tomen tosum and P. caerulea during early stages of gynoecium development. In the case of P. caerulea they lead to development of the corolla tube, but in the case of Rh. tomentosum they do not receive further develop ment. The corolla of L. procumbens appears at first as a meristematic ring, while distinguishable peaks of five petals appearlater. So the corolla tube develops due to early congenital petal fusion in L. procumbens and due to late congenital petal fusion in Rh. tomentosum and P. caerulea. Our observations support earlier data [4] on pres ence of a rudimentary corolla tube in Rh. tomentosum. We support the hypothesis that sympetaly was lost in this line of evolution. Choripetaly of Empetrum may be a plesiomorphic condition, because no vestiges of corolla tube were detected throughout all stages of flower development. However, a complete loss of corolla tube cannot be excluded. CONCLUSIONS Choripetaly of Rhododendron tomentosum is the result of a secondary loss of the corolla tube. Choripe taly of Empetrum could be a plesiomorphic condition
or a result of strong secondary modifications of flower groundplan. We report occurrence of different types of sym petaly in closely related members of basal asterids belonging to the family Ericaceae (Loiseleuria proc umbens and Phyllodoce caerulea). In contrast, in euas terids, the type of sympetaly appears to characterize taxa of higher rank. Variation of sympetaly type is probably an archaic feature. The author thanks to D.D. Sokoloff for guidance and aid in research. This study was supported by grants of President of Russia (MD2644.2009.4), RFBR (090401155) and Ministry of Science and Education of Russia (FCP “Kadry”). REFERENCES 1. Harmaja, H., New Names and Nomenclatural Combi nations in Rhododendron (Ericaceae), Ann. Bot. Fen nici, 1990, vol. 27, no. 2, pp. 203–204. 2. Kron, K.A., Judd, W.S., Stevens, P.F., Crayn, D.M., Anderberg, A.A., Gadek, P.A., Quinn, C.J., and Luteyn, J.L., Phylogenetic Classification of Ericaceae: Molecular and Morphological Evidence, Bot. Rev., 2002, vol. 68, no. 3, pp. 335–423. 3. Leins, P. and Erbar, C., Floral Developmental Studies: Some Old and New Questions, Int. J. Plant Sci., 1997, vol. 158, no. 6, pp. S3–S12. 4. Leins, P., Entwicklungsgeschichtliche Studien an Eri calesBluten, Bot. Jahrb. Syst., 1964, vol. 83, pp. 57– 88. 5. Sedova, E.A. and Vasilevskaya, N.V., Multiplicity of Ontogenetic Processes of Phyllodoce caerulea (L.) Bab. (Ericaceae Juss.) in Subarctic Mountain Tundra, Vestn. Mosk. Univ., Ser. Biol.., 2003, no. 2, pp. 44–49. 6. Sokolov, D.D., Remizova, M.V., Timonin, A.K., and Oskol’skii, A.A., Fusion of Organs in Flowers of Angiosperms: Typology, Taxonomic and Phylogenetic Significance, in Voprosy obshchei botaniki: traditsii i perspektivy: Mater. Mezhdunar. Nauch. Konf., Posv yashch. 200letiyu Kazanskoi botanicheskoi shkoly (23– 27 yanvarya 2006 g.) (Proc. Int. Sci. Conf. Dedicated to the 200th Anniversary of Kazan Botanical School, January 23–27, 2006), Kazan, 2006, pp. 99–101.
MOSCOW UNIVERSITY BIOLOGICAL SCIENCES BULLETIN
Vol. 66
No. 2
2011
