Sciaphila kozushimensis Suetsugu, 2020

Suetsugu, Kenji & Kinoshita, Akihiko, 2020, Sciaphila kozushimensis (Triuridaceae), a new mycoheterotrophic plant from Kozu Island, Izu Islands, Japan, based on morphological and molecular data, Phytotaxa 436 (2), pp. 157-166 : 159-162

Sciaphila kozushimensis Suetsugu , sp. nov. ( Figs. 1–4 )

Type:— JAPAN. Tokyo Metropolis., Kozu Island , 27 June 2018, K. Suetsugu KS 300 (holotype TNS! [herbarium sheet and spirit collection]; isotypes KYO! [herbarium sheet and spirit collection]) .

Diagnosis:— Sciaphila kozushimensis is close to S. tosaensis and S. megastyla but differs in smaller male flowers, wide and acuminate male perianth segments and somewhat dissimilar perianth segments

Monoecious, mycoheterotrophic, perennial herb. Roots filiform, hairy. Stems erect, underground parts white, aerial parts reddish purple, simple or branched at the base, 4–8 cm tall. Scale leaves ovate to narrowly ovate, 2–3 mm long. Inflorescence racemose, rachis 0.5–2 cm long, 3–12-flowered, secund, alternately densely arranged, male flowers towards the apex of the rachis, female flowers towards the base of the rachis. Bracts ovate, scale-like, acute, 2–3 mm long, appressed to the pedicel. Pedicels 1.5–3.5 mm long, patent at 40–80°, straight. Male flowers (2.3–) 3.1–5.1 mm in diam., perianth segments (4–)5–6, somewhat uneven, acuminate to ovate-acuminate, 0.8–2.3 mm long, 0.5–0.8 mm wide at the base, fused basally, opening to a flat plane at the base. Stamens 2–3, sessile; anthers 2-locular, 0.5–0.7 mm long. Female flowers 2.9–4.8 mm in diam., 6–7, somewhat dissimilar, ovate-acuminate to ovate, 1.8–2.5 mm long, 0.5–1.0 mm wide at the base, fused basally. Carpels usually more than 30, ellipsoidal, ca. 0.6 mm long, rounded at apex; style and stigma 0.6–0.7 mm long, clavate, papillate, laterally inserted at a little above the base of ovary.

Distribution and phenology:— Sciaphila kozushimensis is restricted to the type locality on Kozu Island and was found in a dense forest dominated by Castanopsis sieboldii (Makino) Hatusima (1971: 223) . Flowering plants were observed from late-June to mid-July, and fruiting from late-July to mid-August.

Conservation status:— A single location with a population of less than 50 flowering individuals is known on Kozu Island. Therefore, S. kozushimensis should be assigned a risk of extinction of “Critically Endangered” [CR B1ab(iii)+B2ab(iii)+D1] following the IUCN Red List Categories and Criteria ( IUCN 2012). However, it should be noted that the new species can occur more widely because mycoheterotrophic plants, including Sciaphila species, are difficult to find, due to their dwarf habit. In addition, S. kozushimensis can be confused with the more wellknown S. tosaensis , which has a similar gross morphology. Further surveys may reveal a broader distribution of S. kozushimensis .

In this respect, the high genetic differences among S. kozushimensis , S. tosaensis and S. megastyla is remarkable because many endemic species on the Izu Islands have lower level of morphological and genetic differentiation with the mainland progenitors on Honshu Island reflecting the proximity of the islands to the mainland and young age and formation process of the Izu Islands that formed less than 2–3 million years ago ( Nakahama et al. 2019, Yamada & Maki 2012). Therefore, it is possible that S. kozushimensis had not originated in the Izu Islands but in other areas, and subsequently colonized in Kozu Island. Since our phylogenetic analysis strongly suggested that S. kozushimensis was sister to S. megastyla distributed in Ryukyu Islands and Taiwan, it is worth investigating whether S. kozushimensis occurs in these areas.

Taxonomic notes:— Sciaphila kozushimensis is most similar to S. tosaensis in having unisexual flowers (the male flowers towards the apex of the rachis and female flowers towards the base of the rachis), perianth-segments without any appendages, 3 stamens, club-shaped style that is as long as or slightly exceeds ovary in the flowering stage ( Giesen 1938, Makino 1905, Ohashi 2000, Ohashi et al. 2008). However, Sciaphila kozushimensis differs from S. tosaensis in smaller male flowers (3.1–5.1 mm vs. 5.5–6.5 mm), wide and acuminate male perianth segments (acuminate to ovate-acuminate, 0.5–0.8 mm wide at the base vs. narrowly triangular to linearly triangular, 0.2–0.3 mm wide at the base) and somewhat dissimilar perianth segments (vs. equal perianth segments). It is also notable that female perianth segments of S. kozushimensis is as long as male ones, while female perianth segments of S. tosaensis are distinctly shorter than male ones ( Ohashi et al. 2008). In addition, S. kozushimensis is also similar to S. megastyla but S. megastyla can be easily distinguished from the other Sciaphila species, in having very conspicuous style and stigma, as indicated by its specific epithet ( Fukuyama 1936, Suetsugu et al. 2019a). For a detailed comparison of morphological characters among S. kozushimensis , S. megastyla and S. tosaensis , see Table 2.

Molecular analysis:— The ITS matrix contained 17 sequences and 1055 aligned bases, of which 624bp were identified as poorly aligned by Gblocks. All poorly-aligned sites were excluded before phylogenetic analyses. The resultant ITS alignment was 431bp, with 147 variable and 120 parsimony informative sites. ML and NJ analyses yielded similar tree topologies, and only the tree inferred from the ML analysis is shown in Figure 5 . It is notable that two main Sciaphila clades ( S. secundiflora complex and S. nana complex) showed a long branch attraction even within the same genus. While it is not uncommon to see very divergent sequences among mycoheterotrophic taxa ( Merckx et al. 2013), it is possible that different ITS copies with heterogeneity rates of molecular evolution are compared here. It is worth analyzing other DNA loci such as single copy gene to explore more accurate phylogenetic relationships within the genus Sciaphila for future study.

Anyway, phylogenetic analysis of ITS sequences revealed five well-supported lineages within Sciaphila , irrespective of the method used (ML and NJ analyses). The three lineages, i.e., S. kozushimensis , S. megastyla and S. tosaensis clustered with strong branching supports (96/100); a clade with three sequences of S. kozushimensis was sister to S. megastyla (70/66) and they further branched into S. tosaensis . The three ITS sequences of S. kozushimensis (558bp, 559bp and 588bp) showed that 3.2–3.6% variations with S. megastyla from Lanyu, Taiwan (type locality) and 6.8–7.4% variations with S. tosaensis from Kochi, Japan (near the type locality). In contrast, the intraspecific variability of ITS sequences for five Sciaphila species is within 0–0.2%, in spite of the large distance between the sampling sites within the same species (Table 1). In particular, it is notable that ITS sequences of two Sciaphila yakushimensis varieties are identical, despite the morphological differences ( Suetsugu et al. 2019b). Therefore, we concluded that S. kozushimensis is genetically greatly differentiated from these morphologically similar taxa. These molecular data support that the morphological differences among S. kozushimensis , S. megastyla and S. tosaensis are mirrored by their genetic distances.

Additional specimens examined: — JAPAN. Tokyo Metropolis: Kozu Island, 27 June 2018, K. Suetsugu KS305 (TNS [spirit collection]). Kozu Island, 1 July 2018, M. Ishibashi MI86-KS313 (TNS [spirit collection]).

Figures

FIGURE 1. Flowering plants of Sciaphila kozushimensis from type locality.

FIGURE 2. Sciaphila kozushimensis from type locality.A. Rachis. B–H. Male flower. I–J. Female flower (I. Above view. J. Bottom view). K. Immature carpel with stigma. G. Immature fruit. Bar = 2 mm (A), 1 mm (B–J) and 0.5 mm (K).

FIGURE 3. A flowering plant of Sciaphila kozushimensis (drawn from the holotype). Drawn by Kumi Hamasaki. Bar = 1 cm.

FIGURE 4. Sciaphila kozushimensis (drawn from the holotype). A. Flowering plant. B–C. Female flower. D–I. Male flower. J–K. Immature carpel with stigma. G. Immature fruits. Bar = 1 cm (A), 1 mm (B–I) and 0.3 mm (J–K). Drawn by Kumi Hamasaki.

FIGURE 5. Maximum likelihood phylogeny of Sciaphila kozushimensis (bold) and its related taxa based on the rDNA ITS sequences. Maximum likelihood and neighbor-joining branching supports are indicated below branches as ML/NJ.