congresos y reuniones científicas
Scape anatomy, fruit dehiscence, and chromosome numbers support polyphyly of Neomarica (Iridiaceae) and parallel evolution of the leaf-like scape
Congreso; XVIII International Botanical Congress; 2011
Institución organizadora:
University of Melbourne
The family Iridaceae Juss. is composed of ca. 66 genera and 2,030 species. The neotropical tribe Trimezieae Rav. is probably monophyletic, but the delimitation of its currently accepted four genera is still uncertain. Neomarica Sprague is the largest genus of this tribe with ca. 24 species. It is characterized mainly by the broadly flattened scape, morphologically very similar to the leaves, formerly considered a synapomorphy of the genus. Recent studies on fruit morphology, chromosome numbers and phylogeny using DNA sequence data, however, pointed to the possibility that the genus is polyphyletic and its species belong to three not closely related clades. This suggests that the characteristic kind of scape might have evolved three times in the tribe and is a false synapomorphy for the genus. We therefore investigated the anatomy of the scapes to verify if anatomical data would support the idea of parallel evolution of a broadly flattened scape in the groups of Neomarica. Anatomical sections of the scapes of 12 species of Neomarica belonging to the three clades and of 5 species of Trimezia were made by hand and stained with safranine /astra blue. The sections were immersed in glycerin jelly and on the following day studied and photographed in a microscope. We found two different types of scape anatomy agreeing with the findings of different and not closely groups of Neomarica based on the phylogenetic analysis of DNA sequence data, capsule morphology and chromosome number. One type is characterized by an abrupt constriction of the peripheral parts of the scape into two wings, which may be short or elongated. In most species, this wing formation is correlated with a thick peripheral sclerenchymatic ring in the scape closed in the region where the wings are located. The wings of these scapes are very thin and mainly build of sclerenchyma and vascular bundles. The chromosome number of the plants with this anatomy is 2n=32 and the dehiscence of the fruits occurs only at the apex. In the second type, the peripheral parts of the scape narrow gradually to form elongated wings and the sclerenchymatic ring is open at exactly these regions. The wings of these scapes are build of parenchyma with scattered vascular bundles. The chromosome number of these plants is 2n=18 and the fruit dehisces, so far as known, completely down to the base. The first type is typical for Neomarica spp. belonging to the group presumably sister to the genus Trimezia and for N. rupestris, which is more closely related to the genus Pseudotrimezia. The scape of Trimezia spp. is either completely wingless or presents only very short wings. The sclerenchymatic ring here is always closed, which probably represents the plesiomorphic scape anatomy in the tribe. The second type characterizes species of Neomarica s.s. Our study once more demonstrates that phylogenies obtained from molecular data may provoke interesting character re-evaluations of morphoanatomical characters.