Abstract Detail

Ecophysiology

Cameron, Kenneth [1], Giraldo, Giovanny [2].

Phylogeny and Eco-physiology of the Net-veined Vanilloid Orchids.

Despite its relatively small size the orchid tribe Vanilleae of subfamily Vanilloideae exhibits a wide range of vegetative morphologies and life history strategies. Five of the nine genera are leafless, achlorophyllous mycoheterotrophs; three of those are vines. Two additional genera are also climbers but these are mostly leafy and photosynthetic, including the genus Vanilla. The remaining two genera are non-climbing, leafy, tropical herbs. Three of the four leafy taxa in this clade are remarkable for their highly reticulate leaf venation. Clematepistephium smilacifolium, endemic to New Caledonia, is not unlike other monocots that have evolved net-venation in that it is an evergreen vine adapted to shady forest habitats. Its sister taxon, Eriaxis rigida, in contrast, grows as an erect herb in full sun savannas throughout New Caledonia, but has retained its reticulate leaf venation. This is also the case for their close relatives in South American, Epistephium species. After reconstructing the phylogeny of these orchids using anchored phylogenomics we undertook an eco-physiological study that quantified light intensity in the field, leaf area, leaf angle, leaf thickness, fresh and dry leaf mass, plus leaf mass per area for all three genera. We also measured total leaf nitrogen, C12:C13 ratios, and several traits related to their foliar vascular systems, including mean vein density, number of skeleton branching points per leaf area, and areole area, among others. Through these metrics we demonstrated that the growth form and physiology of Clematepistephium is consistent with what is expected of a plant that has adapted to shade; its leaf mass/area indicates that it functions like an evergreen shrub. In comparison, we propose that although they grow in sunny, open habitats, both Eriaxis and Epistephium have retained the net-venation of a shade adapted ancestor, and compensate for their presumably maladaptive leaf structure in different ways on different continents. The former behaves not unlike an evergreen tree, whereas the latter functions physiologically like grasses and other non-woody herbs. This study opens the door to future research on the eco-physiology of the agriculturally important genus Vanilla.

1 - University Of Wisconsin, Department Of Botany, 154 Birge Hall, 450 Lincoln Drive, Madison, WI, 53706, United States
2 - University of Wisconsin, Botany, Madison, WI, 53706, USA

Keywords:
Orchidaceae
evolution
ecophysiology
phylogenomics.

Presentation Type: Oral Paper
Session: ECOPH1, Ecophysiology I
Location: San Pedro 2/Starr Pass
Date: Tuesday, July 30th, 2019
Time: 10:15 AM
Number: ECOPH1006
Abstract ID:579
Candidate for Awards:None