Comprehensive phylogenetic analyses of Orchidaceae using nuclear genes and evolutionary insights into epiphytism

Orchidaceae (with >28,000 orchid species) are one of the two largest plant families, with economically and ecologically important species, and occupy global and diverse niches with primary distribution in rainforests. Among orchids, 70% grow on other plants as epiphytes; epiphytes contribute up to ~50% of the plant diversity in rainforests and provide food and shelter for diverse animals and microbes, thereby contributing to the health of these ecosystems. Orchids account for over two-thirds of vascular epiphytes and provide an excellent model for studying evolution of epiphytism. Extensive phylogenetic studies of Orchidaceae and subgroups have ;been crucial for understanding relationships among many orchid lineages, although some uncertainties remain. For example, in the largest subfamily Epidendroideae with nearly all epiphytic orchids, relationships among some tribes and many subtribes are still controversial, hampering evolutionary analyses of epiphytism. Here we obtained 1,450 low-copy nuclear genes from 610 orchid species, including 431 with newly generated transcriptomes, and used them for the reconstruction of robust Orchidaceae phylogenetic trees with highly supported placements of tribes and subtribes. We also provide generally well-supported phylogenetic placements of 131 genera and 437 species that were not sampled by previous plastid and nuclear phylogenomic studies. Molecular clock analyses estimated the Orchidaceae origin at ~132 million years ago (Ma) and divergences of most subtribes from 52 to 29 Ma. Character reconstruction supports at least 14 parallel origins of epiphytism; one such origin was placed at the most recent common ancestor of ~95% of epiphytic orchids and linked to modern rainforests. Ten occurrences of rapid increase in the diversification rate were detected within Epidendroideae near and after the K-Pg boundary, contributing to ~80% of the Orchidaceae diversity. This study provides a robust and the largest family-wide Orchidaceae nuclear phylogenetic tree thus far and new insights into the evolution of epiphytism in vascular plants.

Harnessing the power of botanical gardens: Evaluating the costs and resources needed for exceptional plant conservation

PREMISE

The effective ex situ conservation of exceptional plants, whether in living collections or cryo-collections, requires more resources than the conservation of other species. Because of their expertise with rare plants, botanical gardens are well positioned to lead this effort, but a well-developed strategy requires a clear understanding of the resources needed.

METHODS

Grant funding was obtained from the Institute of Museum and Library Services to support a three-year project on cryobanking, and to provide smaller grants to 10 other botanical gardens for one-year projects on either (1) seed behavior studies or (2) the development of protocols for in vitro propagation or cryopreservation.

RESULTS

Nine of the partner gardens worked on 19 species (one was unable to continue due to the COVID-19 pandemic), while the larger project focused on 14 species. A point system was developed for tasks accomplished, and the average costs per point of the larger and smaller projects were similar. Labor accounted for half the costs. Projects focused on species in the Asteraceae and Orchidaceae had lower costs per point than other species.

DISCUSSION

Both large and small projects can contribute to a strategy for exceptional plant conservation for similar costs. Prioritizing species with lower costs could help advance the field while allowing time for work on more difficult species to develop.

Microsatellite primers for two threatened orchids in Florida: Encyclia tampensis and Cyrtopodium punctatum (Orchidaceae)

PREMISE OF THE STUDY

The Million Orchid Project at Fairchild Tropical Botanic Garden is an initiative to propagate native orchids for reintroduction into Miami's urban landscapes. The aim of this study was to develop microsatellites for Encyclia tampensis and Cyrtopodium punctatum (Orchidaceae).

METHODS AND RESULTS

Ten microsatellites were developed for each species. For E. tampensis sampled from the natural population, allele numbers ranged from one to four, with an average observed heterozygosity (H o) of 0.314 and average expected heterozygosity (H e) of 0.281. For the individuals from cultivation, allele numbers ranged from one to six, with an average H o of 0.35 and an average H e of 0.224. For C. punctatum, allele numbers ranged from one to three, with an average H o of 0.257 and an average H e of 0.272.

CONCLUSIONS

These microsatellites will be used to assess the genetic diversity of natural and cultivated populations with the intention of guiding genetic breeding under the Million Orchid Project.