Thismia kobensis Suetsugu, 2018

Suetsugu, Kenji, Nakanishi, Osamu, Kobayashi, Tomiki & Kurosaki, Nobuhira, 2018, Thismia kobensis (Burmanniaceae), a new and presumably extinct species from Hyogo Prefecture, Japan, Phytotaxa 369 (2), pp. 121-125 : 121-124

Thismia kobensis Suetsugu , sp. nov. ( Figs. 1 , 2 )

Type:— JAPAN, Hyogo Prefecture, Kobe City, Nishi-ku, Oshibedani-cho, Komi, 34°44’ N, 135°05’ E, 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.

Terrestrial, achlorophyllous, mycoheterotrophic herbs. Roots creeping, vermiform, branched, ca. 1 mm in diameter, whitish when young, pale brown when old. Stem erect, ca. 1 mm long. Leaves glabrous, whitish, scale-like, narrowly triangular to ovate, 1.0–5.0 × 0.4–3.0 mm, apex obtuse to acute; largest leaves just below flower. Involucral bracts, white, similar to upper leaves. Flower solitary, subsessile, pubescent. Perianth actinomorphic with 6 tepals fused to form a basal perianth tube. Perianth tube white, hexagonal prismatic apically and urceolate basally, 8 × 3–7 mm, narrowing just above the ovary, widest at the upper apex; inner surface without transverse bars; apex with a broad, prominent, hexagonal annulus. Inner tepals 3, larger than outer tepals, white, ca. 5.4 × 1.1–1.3 mm, arching inward distally and connate apically to resemble a mitre, apex acuminate; outer tepals 3, white, ca. 4 × 1 mm, apex acuminate. Stamens 6, free from each other, pendulous from the annulus, annulus dark orange, connective yellow; each stamen rectangular with 4 thecae; each theca oblong, ca. 0.6 × 0.1 mm; nectariferous gland absent; connective of stamens without lateral appendages, not forming a skirt-like appendage; apex of each stamen truncate with long hairs. Ovary inferior, cup-shaped, 2.5 × 1.5 mm, pubescent; style ca. 0.45 mm long; stigma trilobed, ca. 1.0 mm long; stigma lobes triangular or arrow-shaped with a long hair on each lobe.

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), T. 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 Rodwaaa ( 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.

Figures

FIGURE 1. Thismia kobensis (holotype) from the type locality.

FIGURE 2. Thismia kobensis (from the holotype). A–B. Flowering plant. C. Flower, upper view. D. Flattened perianth tube. E. Stamens, inner view. F. Stamens, outer view. G. Style and stigma. Two broken inner perianth lobes are indicated by the dotted lines in A, B and D. Drawn by Kumi Hamasaki. Bar = 1 mm.