Few studies document plants in caves. Our field observations of a widespread and seemingly angiosperm-rich cave flora in SW China lead us to test the following hypotheses, 1) SW China caves contain a diverse vascular plant flora, 2) that this is a relic of a largely absent forest type lacking endemic species, and 3) that the light environment plants occupy in caves is not distinct from non-cave habitats. To do so we surveyed 61 caves and used species accumulation curves (SAC) to estimate the total diversity of this flora and used a subsample of 14 caves to characterise the light environment. We used regional floras and existing conservation assessments to evaluate the conservation value of this flora. We used observations on human disturbance within caves to evaluate anthropogenic activities. Four-hundred-and-eighteen vascular plant species were documented with SACs predicting a total diversity of 529–846. Ninety-three percent of the species documented are known karst forest species, 7% are endemic to caves and 81% of the species are angiosperms. We demonstrate that the light environment in caves is distinct to that of terrestrial habitats and that a subset of the flora likely grow in the lowest light levels documented for vascularised plants. Our results suggest that the proportion of species threatened with extinction is like that for the terrestrial habitat and that almost half of the entrance caverns sampled showed signs of human disturbance. We believe that this is the first time that such an extensive sample of cave flora has been undertaken and that such a diverse vascular plant flora has been observed in caves which we predict occurs elsewhere in SE Asia. We argue that the cave flora is an extension of the karst forest understory present prior to catastrophic deforestation in the 20thC. We suggest that within SW China caves serve as both refuges and a valuable source of germplasm for the restoration of karst forest. We also propose that caves represent a distinct habitat for plants that is most similar to that of the forest understory, but distinct with respect to the absence of trees, leaf litter, root mats, higher levels of atmospheric CO2, and lower diurnal and annual variation in temperature and humidity. We highlight tourism, agriculture and the absence of legislated protection of caves as the main current threats to this flora.

Elatostema (Urticaceae) comprises several hundred herbaceous species distributed in tropical and subtropical Africa, Asia, Australia and Oceania. The greatest species richness occurs on limestone karst in Southeast Asia. Taxonomic revisions of Elatostema are largely out of date and contradict each other with respect to the delimitation of Elatostema and Pellionia. Most herbaria in SE Asia and worldwide contain significant amounts of unidentified material. As part of a broader revision of Elatostema in SE Asia, we present an updated checklist for Vietnam based on field visits, a review of specimens in herbaria worldwide, a review of type material and nomenclature. We recognize 77 taxa (75 species and two infraspecific taxa) of Elatostema in Vietnam, 23 of which were previously ascribed to Pellionia. Nineteen of these are new records for the country, i.e., E. attenuatoides, E. austrosinense, E. backeri, E. brunneinerve, E. crassiusculum, E. crenatum, E. fengshanense, E. glochidioides, E. malacotrichum, E. nanchuanense, E. oblongifolium, E. obtusum, E. oppositum, E. pergameneum, E. prunifolium, E. pseudolongipes, E. pycnodontum, E. salvinioides and E. xichouense. We place E. baviensis in synonymy of E. platyphyllum, E. colaniae in synonymy of E. myrtillus, P. macroceras in synonymy of E. hookerianum, and P. tetramera in synonymy of E. dissectum for the first time. Fourteen taxa (18% of all the recognized taxa) are endemic to Vietnam, which makes Elatostema one of the richest genera for endemic species in this country; this level of endemism is comparable to levels observed in Orchidaceae. Our checklist suggests that the highest diversity and endemism of Elatostema occurs in northern Vietnam, and that there is the greatest floristic similarity of northern Vietnam to SW China. The relationship among floristic regions is also investigated. We could find no records of Elatostema for 33 out of 63 provincial units of Vietnam, including all the southernmost provinces. We propose that further studies on the diversity of Elatostema in central and southern Vietnam are severely needed.

Ensuring that genera are monophyletic should result in a stable classification that better reflects evolutionary history, and which can serve as a framework for answering broader scientific questions. It is also important that species can be assigned to genera easily and unambiguously so as to remove barriers to identification and species discovery. Pilea, with 933 published names and likely more than 700 spp. is the largest genus within the Urticaceae and was last monographed in 1869. Whilst the monophyly of the genus has been proposed by previous authors, this has been based on incomplete taxon sampling that has failed to resolve the position of key taxa. We aimed to generate a robust phylogeny for Pilea and allied genera that could test the monophyly of the genus and provide a framework for a taxonomic revision of this species‐rich yet poorly studied genus. To do so, we sought to sample taxa encompassing previous infrageneric classifications and species with anomalous inflorescences or flower morphology and to use the resulting phylogeny to evaluate the delimitation of Pilea and to establish an infrageneric classification. In addition, we included a representative of the Polynesian genus Haroldiella, which, morphologically, seemed indistinguishable from Pilea. Using two plastid and one nuclear region, we constructed phylogenies using Bayesian inference, maximum likelihood and maximum parsimony approaches. We used our BI phylogeny to evaluate the informativeness of 22 morphological characters and used both to delimit monophyletic groups and infrageneric sections. Our results recovered Pilea as paraphyletic, a consequence of the recovery of a monophyletic clade comprising Lecanthus and Pilea sect. Achudemia and sect. Smithiella, neither of which had been adequately sampled in previous studies. We also recovered Pilea as paraphyletic with respect to Haroldiella. Pilea (including Haroldiella) was recovered as sister to the clade comprising Lecanthus and Pilea sect. Achudemia and sect. Smithiella. We identified isomery between male and female flowers, flower part number, male sepal arrangement and achene ornamentation as being phylogenetically informative characters that can be used to distinguish Achudemia (Pilea sect. Achudemia and sect. Smithiella) from Pilea. We also identified a trend of decreasing merism and fruit size, correlated with an increase in species‐richness across the phylogeny which our results suggest may indicate a shift in pollen and fruit dispersal, pollen dispersal becoming more kinetic and fruit dispersal less reliant on animals. On the basis of our evaluation of both morphological characters and phylogenetic relationships we propose a new infrageneric classification for the genus comprising eight sections, five of which we propose for the first time here: Pilea sect. Angulatae, sect. Plataniflorae, sect. Tetraphyllae, sect. Trimeris and sect. Verrucosae.