Taxonomic Notes on Didymoplexiella siamensis and Gastrodia peichatieniana, Two Fully Mycoheterotrophic Orchids New to the Flora of Hong Kong
Abstract
The ephemeral, leafless orchids Didymoplexiella siamensis and Gastrodia peichatieniana are newly recorded from Hong Kong. A lectotype is selected for the former, and the recently described D. denticulata from southern Vietnam is reduced to its synonymy. Full descriptions and global conservation assessments are presented for these hitherto poorly known species.
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- The mycoheterotrophic orchid genera Didymoplexiella Garay (1955: 33) and Didymoplexis Griffith (1844: 383) include seven and ca. 20 species, respectively (Averyanov 2011, Hu et al. 2014, Tsukaya et al. 2014, Suetsugu et al. 2017). Didymoplexiella is similar in both habit and floral appearance to Didymoplexis, with which it was considered congeneric by some earlier authors (Smith 1920, Holttum 1953). However, modern taxonomists generally agreed that Didymoplexiella species can be distinguished from Didymoplexis species by the presence of a pair of long recurved stelidia on the tip of the column and the absence of a distinct column foot (Garay 1954, Seidenfaden 1978, Seidenfaden & Wood 1992, Su 2000, Comber 2001, Jin et al. 2004, Pridgeon et al. 2005, Tsukaya et al. 2005, 2014, Chen et al. 2009, Rojchana-Umpawan et al. 2014, Yokota et al. 2016).
- Taiwania 55: 92. 2010, syn. nov. — Type: Vietnam. Quang Binh Province
- Didymoplexiella
- L Aver
- P K Averyanov
- N T Loc
- Vinh
Didymoplexiella denticulata Aver., Taiwania 55: 92. 2010, syn. nov. — Type: Vietnam. Quang Binh Province, Le Thuy District, 150–200 m, 9 April 2008, L. Averyanov, P.K. Loc, N.T. Vinh et al., HAL 11443 (holotype HN, photo!; isotype LE, photo!). - Three new orchid species are described from Vietnam as a new for science. They are - Cheirostylis cristata (related to C. bipunctata and C. chinensis), Didymoplexiella denticulata (related to D. ornata and D. siamensis) and Habenaria luceana (similar superficially to H. geniculata, H. ecalcarata, H. malintana and H. parageniculata, but having rather isolated taxonomic position). Detailed description, illustrations, data on flowering time, ecology and distribution are provided for each recognized species.
- In this chapter, we discuss the current knowledge of the evolution and diversification history of mycoheterotrophic plants, including aspects about the origin of mycoheterotrophy, and common evolutionary trends in mycoheterotrophic lineages. While phylogenetic reconstruction of mycoheterotrophic plant relationships is hampered by the rarity of the taxa and high rates of DNA substitutions, current evidence shows that all mycoheterotrophic plant lineages arose from autotrophic mycorrhizal ancestors. Mycoheterotrophic interactions evolved independently in nearly all of the major land plant lineages and let to at least 46 independent origins of full mycoheterotrophy. In some groups there is evidence that full mycoheterotrophy is preceded by partial and initial mycoheterotrophy. Clades of fully mycoheterotrophic species are in some cases ancient, which demonstrates that full mycoheterotrophs can persist and diversify over a considerable amount of evolutionary time. However, even ancient lineages of full mycoheterotrophs contain relatively few species which suggests that speciation rates are low, extinction rates are high, or a combination of both processes. Shifts to full mycoheterotrophy are often accompanied by parallel evolutionary trends, including the reduction of vegetative parts, reduction of seed size and seed complexity, shifts to more shaded habitats, high rates of molecular evolution, and increased mycorrhizal specificity.
- The jewel orchid Cheirostylis pusilla Lindl. is newly recorded from Hong Kong, a significant distance from Yunnan Province, the only other confirmed locality for the species in China. A full description, photos and line drawings are presented for this hitherto poorly known species, and its conservation status is assessed. Cheirostylis malleifera C. S. P. Parish & Rchb. f. is shown to be a later synonym.
- The record of species descriptions within a taxonomic group represents the product of a sampling process. How useful such a record is in inferences about biodiversity and evolutionary patterns can depend on the nature of this sampling process. Here we describe a test for two potential biases: the novelty bias, the preferential description of species from higher taxa with relatively few previously described species; and the familiarity bias, the preferential description of species from already described higher taxa. At the heart of the test is the determination of whether the description of the higher taxa proceeded at a rate faster (the novelty bias) or slower (the familiarity bias) than expected by chance given the total number of species described for each higher taxon. Ambiguity may arise if there is uncertainty in the exact order in which new species and higher taxa were described. We apply the test to description records for eight groups of orchids. A novelty bias is detected in two to three cases and familiarity bias may be present in one case. The results are discussed in relation to perception of morphological complexity and the potential for human vision‐based bias in biodiversity assessments.
- In continuation of earlier papers in this series, published in the now discontinued Botanisk Tidskrift Vol. 65–72, 1969–1977, additions and corrections to earlier papers on East Asiatic orchids are supplied. Seven new species are proposed, of which five from neighboring countries, and further seven new records for Thailand are listed. The five species alien to Thailand may be expected to be found also in Thailand. Some nomenclatural changes and new synonyms are proposed. An attempt is made to clarify taxonomical and nomenclatural problems on some entities in the Rhopalanthe section of Dendrobium.
- Aim To examine which aspects of primates and carnivore biology can be used to predict attributes of species yet to be discovered. Location Global. Methods Multiple regressions of phylogenetically independent contrasts and non-phylogenetic species date of description, on multiple biological predictor variables, formed from previous hypotheses tested in the literature. Results Orders differ, but both carnivore and primate species with a large geographical range tend to have been discovered earlier. When geographical range is controlled for, body mass is also significantly correlated with description date in carnivores, but remains a poor predictor in primates. No multiple-predictor model is apparent in the primates, but diurnal species are on average more likely to be described first. Carnivores not endemic to the tropics are more likely to be discovered earlier, reflecting a northern bias in description patterns. Main conclusions Geographical range is by far the most important predictor variable. The study may have ramifications for conservation hotspot selection: species possessing a small geographical range are least likely to have been described, yet are most heavily weighted in some hotspot selection algorithms.
- Nonphotosynthetic mycorrhizal plants have long attracted the curiosity of botanists and mycologists, and they have been a target for unabated controversy and speculation. In fact, these puzzling plants dominated the very beginnings of the field of mycorrhizal biology. However, only recently has the mycorrhizal biology of this diverse group of plants begun to be systematically unravelled, largely following a landmark Tansley review a decade ago and crucial developments in the field of molecular ecology. Here I explore our knowledge of these evolutionarily and ecologically diverse plant-fungal symbioses, highlighting areas where there has been significant progress. The focus is on what is arguably the best understood example, the monotropoid mycorrhizal symbiosis, and the overarching goal is to lay out the questions that remain to be answered about the biology of myco-heterotrophy and epiparasitism.
