Elaiophore diversity in three contrasting members of Oncidiinae (Orchidaceae)

The elaiophores of Trichocentrum cavendishianum (Bateman) M.W. Chase & N.H. Williams, Oncidium loefgrenii Cogn., and Gomesa recurva R. Br. display considerable morphological and anatomical diversity. Oil secretion by flowers of T. cavendishianum and O. loefgrenii can be related to the presence of saddle-like, labellar elaiophores and the labellar callus, respectively, whereas, in G. recurva , although oil is present, no obvious structure appears to be involved in its secretion. In the first two species, the secretory tissue consists of palisade-like cells, whereas, in G. recurva , these cells are oval. Many Oncidiinae are thought to mimic members of the Malpighiaceae, and the elaiophores of that family also contain palisade-like cells that may indicate evolutionary convergence. As oils accumulate below the elaiophore cuticle, that of T. cavendishianum becomes distended, whereas that of the other two species does not. Full discharge of oil from the elaiophores of T. cavendishianum probably occurs only after the cuticle is ruptured by a visiting insect, and this may contribute towards pollinator selection.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 135–148.     

Quaternary climate change and habitat preference shaped the genetic differentiation and phylogeography of Rhodiola sect. Prainia in the southern Qinghai–Tibetan Plateau

There are two long‐standing biogeographic hypotheses regarding the glacial survival of plant species in the Qinghai–Tibetan Plateau (QTP): the in situ survival hypothesis and the tabula rasa hypothesis. We tested these two hypotheses in a phylogeographic study of Rhodiola sect. Prainia, a monophyletic section with ecologically divergent lineages. Molecular data from the nuclear internal transcribed spacer, six plastid markers and 13 nuclear microsatellite loci were analyzed for 240 individuals from 19 populations of this section. Environmental data were used to analyze the niches of major phylogenetic lineages within this section and to model changes in their distributions since the Last Glacial Maximum (LGM). We found that Rhodiola sect. Prainia consists of three evolutionary lineages: all populations of R. stapfii, R. prainii populations at the southern edge of the QTP, and R. prainii populations in the interior part of the QTP. During the LGM, the survival of R. prainii in the interior part of the QTP corresponded with the in situ survival hypothesis, while R. stapfii most probably survived the LGM in a manner corresponding with the tabula rasa hypothesis. The evolutionary history of different lineages of this section was shaped by topography, climate change, and lineage‐specific habitat preferences.