| Thismia kobensis Suetsugu|
in Suetsugu, Nakanishi, Kobayashi & Kurosaki, 2018
Thismia Griffith (1844: 221), Thismiaceae J. Agardh or Burmanniaceae sensu APG VI (2016), is one of the most species-rich mycoheterotrophic genera, consisting of ca. 80 species (Jonker 1948, Merckx et al. 2013). Considering that most of these species were collected only once (Jonker 1948) and that many new species have recently been discovered in various Asian countries (e.g. Suetsugu et al. 2017, 2018), many more undescribed species are likely in these regions.
Oxygyne Schlechter (1906: 140) is a rare, mycoheterotrophic plant genus that consists of six species. It has one of the most remarkable distributions of all angiosperm genera and is disjunct between Japan and western Central Africa (Cheek et al. 2018). Although O. hyodoi Abe & Akasawa (1989: 161) was described based on the specimens discovered in Ehime Prefecture, Kobayashi & Kurosaki (1993) noted that a specimen that was morphologically similar to O. hyodoi was also discovered in Kobe City, Hyogo Prefecture. However, the specimen differed from O. hyodoi in many features. As noted by Tsukaya (2016), characters such as the prominent annulus on the perianth tube suggested that it may not even belong to the genus Oxygyne. In addition, although it was identified as O. hyodoi based on its short perianth lobes (Kurosaki, personal communication), such flowers have also been noted in the genus Thismia (Tsukaya 2016). Therefore, it is highly probable that the specimen collected in Kobe was not O. hyodoi, but a Thismia species (Tsukaya 2016).
So far, only one specimen of the putatively unknown Thismia species has been found, and two of the three inner perianth-lobes in this specimen were broken. In addition, the population was almost certainly destroyed during construction of an industrial complex, and no additional specimens have been found. Fortunately, the other parts of this specimen, including an inner perianth-lobe and all three of the outer perianth-lobes were completely preserved, so we conducted a taxonomic investigation using this specimen. Careful examination revealed that the unknown plant actually belongs to the genus Thismia. Here, we describe it as a new species, Thismia kobensis Suetsugu, as this specimen was found to have a significantly different floral morphology from the other known Thismia species. In addition, the unknown species belonged to the section Rodwaya Schlechter (1921: 38), as it had the vermiform, creeping roots, the inner perianth lobes without free filiform appendages and inner perianth lobes connivent at their apex. Here, we describe it as a new species, with discussions on the taxonomic validity of the section Glaziocharis (Taub. ex Warm.) Hatusima (1976: 4).
|FIGURE 1. Thismia kobensis (holotype) from the type locality.|
Thismia kobensis Suetsugu, sp. nov.
Type:— JAPAN, Hyogo Prefecture, Kobe City, Nishi-ku, Oshibedani-cho, Komi, ...alt. 200 m, 10 June 1992, Nakanishi & Kobayashi 22380 (holotype: HYO, in spirit collection).
Thismia kobensis is close to T. huangii Jiang & Hsieh (2011: 139) from Taiwan but differs in having a hexagonal prismatic perianth tube, white tepals and free stamens
Distribution:— Japan (so far known from only type locality).
Preliminary conservation status:— Extinct (EX). Thisima kobensis is known from only a single individual at Kobe City, Hyogo Prefecture. The specimen was collected in secondary forest dominated by Quercus serrata and Q. glauca in 10 June 1992. Although intensive surveys of the population discovered in June were conducted from 1992 to 1999, we did not discover additional T. kobensis plants. In 1999, the area was completely destroyed during the construction of an industrial complex. Since then, we have searched the surrounding intact areas in June each year but have failed to record any individuals. It is highly likely that the last individual has died, and this taxon is presumed extinct, although we need further efforts to discover additional individuals.
Notes:— According to Jonker (1938), Thismia kobensis belongs to the section Rodwaya, as it has vermiform and creeping roots, inner perianth lobes without free filiform appendages and inner perianth lobes that are connivent apically. In the section Rodwaya, T. kobensis is most similar to T. huangii from Taiwan, in having a dark-orange annulus, yellow and truncate connectives with hairs, stigma lobes with hairs and no nectaries. However, it is easily distinguished from T. huangii in having a hexagonal prismatic and less hairy perianth tube (vs. urn-shaped and densely hairy perianth tube), white tepals (vs. pale orange to yellow), and stamens free from each other (vs. adnate, forming a tube around the style).
In addition, in having the stamens free from each other, T. kobensis is somewhat similar to T. abei (Akasawa) Hatusima (1976: 7) that belongs to the section Glaziocharis. So far, free stamens have not been reported in any species of Thismia except T. abei. However, T. kobensis clearly differs from T. abei in having a hexagonal prismatic perianth tube (vs. urn-shaped perianth tube), dark orange prominent annulus (white inconspicuous annulus), yellow rectangular connective (vs. white spatulate connective), outer perianth lobes without filiform appendages (vs. outer perianth lobes with long filiform appendages). Because appendages of the outer perianth lobes are considered a diagnostic character to distinguish sections Glaziocharis and Rodwaya (Kumar et al. 2017), we believe that T. kobensis is a member of Rodwaya. However, it should also be noted that several recent molecular studies suggested that the appendages of perianth lobes have little systematic significance in Thismia (Hunt et al. 2014, Merckx & Smets 2014, Kumar et al. 2017, Sochor et al. 2018). Actually, molecular results have clearly suggested that section Glaziocharis is not monophyletic and should be incorporated in section Rodwaya (Hunt et al. 2014, Merckx & Smets 2014, Kumar et al. 2017). Both our results (i.e., similarity of stamen morphology between T. kobensis and T. abei) and molecular analyses indicate that it is not necessary to distinguish Glaziocharis and Rodwaya as distict sections.
Given that mycoheterotrophic plants are highly dependent on the activities of both the fungi and the trees that sustain them (Suetsugu et al. 2014, 2017b), they are particularly sensitive to environmental disturbance. Therefore, most mycoheterotrophic species are rare and seriously endangered. Furthermore, our study clearly indicated that some mycoheterotrophic plants have become extinct before being described. As the precise identification of most mycoheterotrophic plants requires detailed observations of floral organs that are hidden in the perianth tube (Tsukaya & Hidayat 2016, Suetsugu 2017a, b), re-examination of herbarium specimens will be useful for understanding both past and current diversity of the mycoheterotrophic flora.
Kenji Suetsugu, Osamu Nakanishi, Tomiki Kobayashi and Nobuhira Kurosaki. 2018. Thismia kobensis (Burmanniaceae), A New and Presumably Extinct Species from Hyogo Prefecture, Japan. Phytotaxa. 369(2); 121–125. DOI: 10.11646/phytotaxa.369.2.6
New plant species discovered in museum is probably extinct kobe-u.ac.jp/research_at_kobe_en/NEWS/news/2018_09_13_01.html | Research at Kobe @KobeU_Global
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