Gastrodia flexistyloides Suetsugu, 2014

Suetsugu, Kenji, 2014, Gastrodia flexistyloides (Orchidaceae), a new mycoheterotrophic plant with complete cleistogamy from Japan, Phytotaxa 175 (5), pp. 270-274 : 270-273

Gastrodia flexistyloides Suetsugu , sp. nov. ( Figs. 1–2 )

Type: — JAPAN. Kyushu: Kagoshima Pref., Takashima Island , 25 March 2014, K . Suetsugu s.n. (holotype KYO; isotype TNS) .

Diagnosis:— Gastrodia flexistyloides differs from its close relative G. flexistyla T.C. Hsu & C.M. Kuo (2010: 243) , in that it has a larger inflorescence, a completely cleistogamous flower, and a smaller, narrower perianth tube.

Terrestrial, mycoheterotrophic herb. Roots few, slender or occasionally thickened, mostly extending from apex of the rhizome. Rhizome tuberous, fusiform or cylindrical, 2–8 cm long, 4–12 mm in diameter, pale brown, covered with numerous scales and unicellular hairs. Inflorescence erect, pale brown, 9–18 cm long, 3–5 mm in diameter, 3–4 nodes, with tubular, membranous sheaths. Bracts up to 8 mm long, 5 mm wide. Pedicel and ovary up to 15 mm long. Flowers 1–6, tubular, slightly upwards or downwards, resupinate, 15–18 mm long, 5–6 mm in diameter. Sepals and petals united forming a five-lobed perianth tube. Perianth tube enclosed or never opening. Sepals subsimilar, fleshy, 15–18 mm long, connate ca. 3/4 of their length with petals, lateral ones connate ca. 2/3 with each other, outer surface pale brown, verrucose; free portion of dorsal sepal ovate-rectangular, apex retuse, ca. 4.5 mm long, 4 mm wide; free portions of lateral sepals ovate, ca. 4.5 mm long, 4.5 mm wide, apex obtuse. Free portions of petals pale orange, ovate, ca. 4 mm long, 3 mm wide, base contracted and thickened, margin slightly scabrous. Lip adnate to column foot, pale green, ca. 8–9 mm long, 4–5 mm wide; hypochile with 2 greenish, globose calli; epichile rhombate-ovate, base contracted, 4–6 ridged on the disc, with two central ridges extending toward the apex, margin slightly undulate; apex portion ligulate, red, ca. 1.5 mm wide. Column 3-lobed, lateral lobes erect, ca. 6 mm long, central lobe strongly incurved; column foot well developed; rostellum absent. Anther hemispheric, ca. 1 mm in diameter, pollinia 2. Capsule cylindrical, 3–3.5 cm long, pedicel elongating to ca. 30 cm long in fruit. Seeds fusiform, ca. 2 mm long.

Distribution: —To date, the distribution of G. flexistyloides appears to be restricted to Takashima Island. The population was located in a bamboo forest dominated by Pleioblastus linearis (Hack.) Nakai.Several hundred flowering individuals were found throughout the island. Flowering was observed from mid-March to early April, and fruiting from early April to early May.

Taxonomic notes:—The remarkable characteristic of G. flexistyloides is its trilobed column, which has a strongly incurved central lobe. In this respect, this species shows great similarity to G. flexistyla T.C. Hsu & C.M. Kuo (2010: 243) from Taiwan, although G. flexistyloides can be distinguished by its larger stature during flowering (9–18 cm vs. 3–6 cm), its floral character (cleistogamous vs. chasmogamous), smaller size (15–18 mm vs. 19–24 mm) and narrower perianth tube (5–6 mm vs. 11–13 mm), as well as the ratio of its petal to sepal length (ca 1:1 vs. 1:1.5–2 for G. flexistyloides and G. flexistyla , respectively).

The most significant difference between these two species is that all the individuals of G. flexistyloides have only cleistogamous flowers, while all observed individuals of G. flexistyla have opening flowers (Tian-Chuan Hsu, pers. comm.). Some orchids utilize both chasmogamous and cleistogamous flowers (e.g. CaraDonna & Ackerman 2012) and some specimens of such species that incidentally have only cleistogamous flowers were mistaken for new taxa (Pupulin and Bogarín 2011). However, such “new species” were always collected in the regions where only equivalent chasmogamous species exists (Pupulin and Bogarín 2011). Gastrodia flexistyloides is distinct from such examples because the hundreds of G. flexistyloides in the Takashima population only produce cleistogamous flowers (complete cleistogamy). Because the morphological dissimilarities are clear and stable, I thus treat this taxon as an independent species rather than an infraspecific taxon of G. flexistyla . This notion is also based on biological species concept, which defines a species as members of populations that actually or potentially interbreed in nature, because complete cleistogamous conditions block gene flow with G. flexistyla . In fact, taxa with complete cleistogamy have often been recognized as species levels and a recent review documents ca. 70 such cases ( Culley & Klooster 2007).

Gastrodia flexistyloides is also similar in appearance to G. takeshimensis Suetsugu (2013: 375) , since both species have completely cleistogamous flowers and elongated corolla tubes. However, the two species differ greatly with regard to their lip and column morphology ( Suetsugu 2013a). In addition, G. flexistyloides can also be distinguished from G. takeshimensis without dissection of the perianth tube as the perianth tube differs in colour (pale brown vs. dark brown for G. flexistyloides and G. takeshimensis , respectively). Furthermore, the flowering season of G. flexistyloides (mid-March to early April) is somewhat earlier than that of G. takeshimensis (late March to late April).

Reproductive biology:— G. flexistyloides adopts an autonomous self-pollination system. Reports of autonomous self-pollination are fairly common in Orchidaceae (e.g. Suetsugu 2013a, b,c, 2014).The usual mechanism of autonomous self-pollination involves the pollinia falling onto the stigma surface, allowing contact between the pollinia and stigma (e.g. Liu et al. 2006, Chen et al. 2012, Suetsugu 2013a, b, c, 2014, but also see Gamisch et al. 2013). However, the autogamous system of G. flexistyloides is notable because the central lobe of the column, which is strongly incurved, also contributes to the pollination process, allowing the anther to contact with stigma directly and thus facilitate selfpollination. So far, this selfing strategy has only been reported in G. flexistyloides and the closely related species G. flexistyla .

The flowers of G. flexistyloides remain closed throughout the flowering period (mid-March to early April). Although cleistogamous plants usually adopt a mixed pollination strategy, also bearing chasmogamous flowers for open pollination (reviewed by Culley & Klooster 2007), it was found that G. flexistyloides only produced cleistogamous flowers, which indicates that it is an obligate self-pollinating species. Complete cleistogamy is also known to occur in several Gastrodia species belonging to section Codonanthus (e.g. G. clausa T. C. Hsu, S. W. Chung & C. M. Kuo (2012: 271) and G. takeshimensis ). In addition, G. flexistyloides also shares a common characteristic with section Codonanthus , producing pedicels that elongate considerably until the dehiscence of the capsules, a feature that is theorized to facilitate the wind dispersal of seeds in Codonanthus ( Pedersen et al. 2004) .

Figures

FIGURE 1. A. Flowering plants of Gastrodia flexistyloides (from the type locality; bar = 2 cm). B. Dissected flower. C. Lip. D–F. Column (D, front view; E, back view; F, lateral view).A. Bar = 2 cm. B. Bar = 5 mm. C–F. Bar = 2 mm.

FIGURE 2. Gastrodia flexistyloides (from the holotype).A. Habit. B–D. Flower. (B, back view; C, front view; D, side view). E. Flattened flower. F. Flattened perianth tube with lip. G. Longitudinal section of the flower. H. Lip. I–K. Column (I, front view; J, back view; K, lateral view).A. Bar = 3 cm. B–G. Bar = 5 mm. I–K = 3 mm. H. Bar = 1 mm.