Gastrodia okinawensis Suetsugu, 2017

Suetsugu, Kenji, 2017, Two new species of Gastrodia (Gastrodieae, Epidendroideae, Orchidaceae) from Okinawa Island, Ryukyu Islands, Japan, Phytotaxa 302 (3), pp. 251-258 : 254-256

Gastrodia okinawensis Suetsugu , sp. nov. ( Figs. 3–4 )

Type: — JAPAN. Ryukyu: Okinawa Pref., Okinawa Island, Kunigami Village, Hungawa, 12 March 2016, Toma, Watanabe, Watanabe s. n. (holotype: KYO!)

Gastrodia okinawensis is similar to G. takeshimensis but is distinguished by having chasmogamous flowers with a paler perianth tube and longer column.

Terrestrial, mycoheterotrophic herbs. Roots few, slender, often produced from the junction between rhizome and inflorescence after the flowering season. Rhizome tuberous, fusiform or cylindrical, 20–60 mm long, 3–10 mm in diameter, yellowish brown, covered with numerous scales and root-hair-like unicellular hairs. Inflorescence erect, pale brown, 10–17 cm long, 2.5–4.0 mm in diameter, 3–4 nodes, with tubular, membranous sheaths. Bracts ovate, up to 6 × 4 mm. Pedicel and ovary up to 10 mm long. Flowers 1–4, tubular, tilted upwards or downwards, resupinate, 18–21 mm long, 6–8 mm in diameter. Sepals and petals united, forming a five-lobed perianth tube. Sepals subsimilar, 18–21 mm long, adnate ca. 4/5 their length with petals, lateral ones connate ca. 4/5 their length, outer surface pale brown with numerous white warty spots, margin entire or slightly undulate; free portion of dorsal sepal straight, ovate-triangular, obtuse at apex, ca. 5 × 5 mm; free portions of lateral sepals, triangular, acute at apex, ca. 5 × 5 mm. Free portions of petals ovate or ellipse, ca 3.0 × 2.5 mm. Lip joined with perianth tube, ca. 10 mm long, hypochile pale green without any appendages or calli; epichile pale greenish yellow to whitish reddish orange, ellipse, base contracted, disc 2 ridged, extended toward the apex, margin slightly undulate; the apical portion ligulate, reddish orange, ca. 1.5 mm wide. Column straight, semi-cylindrical, ca. 10.0 mm long, 2.0– 2.5 mm wide, white; lateral wings (stelidia) distinct, narrow, the edges parallel to column, base slightly angled, apex acute; rostellum absent. Anther hemispheric, 1.0– 1.5 mm in diameter, pollinia 2. Capsule cylindrical, ca. 3 cm long, pedicel elongating to ca. 20–30 cm long in fruit. Seeds fusiform, ca. 2 mm long.

Additional specimens examined: — JAPAN. Ryukyu: Okinawa Pref., Okinawa Island, Azuma Village, Arakawa, 2 Mar. 2012, Suetsugu et al. s.n. ( KYO).

Distribution and phenology:— To date, the distribution of G. okinawensis is restricted to Okinawa Island. Flowering was observed from late February to mid-March, and fruiting from late March through April.

Taxonomic notes:— Gastrodia okinawensis is characterized by having an elongate perianth tube, which belongs to the G. nipponica complex.Among the G. nipponica complex, G. okinawensis is also characterized by relatively taller stature. Therefore, G. okinawensis is morphologically similar to G. takeshimensis , which shares the same characters. However, G. okinawensis can be distinguished by its different floral condition (chasmogamous vs. cleistogamous), colour of the perianth tube (pale brown with numerous white warty spots vs. dark brown), colour of the lip (pale greenish yellow to whitish-reddish orange vs. reddish orange) and length of column (ca. 10 mm vs. ca. 8 mm).

Reproductive notes:— Pollinia of both species described here rapidly fragment into massulae before the flowers mature, which I observed by a careful dissection of flowers at different stages. Therefore, these species have an automatic selfing strategy. Mycoheterotrophic plants are often found growing on the dense forest floor, shaded by woodland or scrub. It can be theorized that mycoheterotrophy developed as an adaptation for these species to survive in such low-light conditions ( Bidartondo et al. 2004). However, such low-light environments are not suited to species of insects commonly associated with pollination, which could limit plant reproduction ( Herrera 1995, 1997). It appears that most mycoheterotrophic species investigated to date (especially nectarless species) have indeed abandoned an insect-mediated pollination system in favor of automatic self-pollination (e.g. Suetsugu 2013a, b, Suetsugu 2014, Suetsugu 2015c).

This strategy can therefore be considered a mechanism that provides reproductive assurance to compensate for pollinator limitation due to their lack of nectar and a habitat hostile to pollinators. In extreme cases, complete cleistogamy can be observed in some Gastrodia species. As suggested by Tsukaya & Hidayat (2016), because both Gastrodia nipponicoides and G. okinawensis open their flowers only slightly, it is possible that these two species also exhibit an evolutionary transitional stage between outcrossing and obligate autogamy.

Figures

FIGURE 3. Gastrodia okinawaensis from the type locality. A. Flowering plants. B. Flower, side view. C. Flower, front view.

FIGURE 4. Gastrodia okinawensis (from the holotype). A. Habit. B. Flower, view from above. C. Flower, side view. D. Flower, bottom view. E. Flower, Front view). F. Flattened perianth tube. G. Flattened lip. H.Anther cap. I. Column, bottom view. J. Column, side view. K. Column, top view).A. Bar = 3 cm., B–D., F. Bar = 1 cm., E, G, I–K. Bar = 5 mm., H = 1 mm.