Aphyllorchis periactinantha A.Chantanaorr. & Chantanaorr., 2022

Chantanaorrapint, Amonrat & Chantanaorrapint, Sahut, 2022, Aphyllorchis periactinantha (Orchidaceae, Neottieae), a new mycoheterotrophic species from peninsular Thailand, PhytoKeys 215, pp. 107-115 : 107

Aphyllorchis periactinantha A.Chantanaorr. & Chantanaorr. sp. nov.

Figs 2 , 3

Diagnosis.

Similar to A. anomala , but differs in having a concave labellum without purple veins, acute at the apex, and a semicircular rostellum.

Type.

Thailand. Songkhla Province: Ton Nga Chang wildlife sanctuary, ca. 100 m, 06°59'43.91"N, 100°09'00.57"E, 26 December 2020, S. Chantanaorrapint & A. Chantanaorrapint 3109 (holotype: BKF!; isotype: PSU! [PSU00019495]) .

Description.

Terrestrial, achlorophyllous herbs, with a suberect rhizome and an erect flowering shoot. Rhizomes pale brown, producing numerous horizontal roots; roots fleshy, 3.5-6.5 mm in diameter, pale brown, glabrous. Flowering shoots 70-150 cm tall, up to 9 mm in diameter at base, unbranched whitish or pale yellow, marked with purple stripes or spots, with 5-9 membranous sheaths at base and 10-15 scales above. Inflorescence racemose, terminal, 15-30 cm long, up to 32 flowers; rachis glabrous. Floral bracts reflexed, lanceolate to linear-lanceolate, acute to acuminate, 16.5-21.5 × 4.5-5.5 mm, whitish or pale yellow with purple stripes. Flowers opening widely, creamy white to pale yellow. Sepals creamy white to pale yellow, minutely tuberculate and sparsely pubescent on the adaxial surface, scattered with purple stripes or dots, concave, margins entire, apex acute; dorsal sepal narrowly ovate to lanceolate, 17.5-19.6 × 4.3-5.2 mm; lateral sepal obliquely narrow-ovate to obliquely lanceolate, 16.8-19.0 × 4.2-5.1 mm. Petals creamy white to pale yellow with purple veins, oblong-lanceolate, 16.0-16.5 × 3.9-4.3 mm, slightly falcate at apex, base obtuse to subtruncate, apex acute, margin entire or minutely erose and slightly recurved backward in the middle, keeled adaxially along midrib. Labellum creamy white to pale yellow, simple and not divided into hypochile and epichile, oblong-lanceolate, 16.2-17.0 × 3.8-4.5 mm, more or less folded along a midrib, concave at the basal part, apex acute, margin nearly entire or minutely erose, abaxial and adaxial surfaces nearly smooth. Column slender, subclavate, yellow at the apical third and purple at the proximal two thirds, gently curved throughout its entire length, 10-12 mm long, without column wing or a hook-shaped appendage on ventral side; clinandrium with a rather large central dome-like outgrowth; stigma more or less ovate in outline, shallowly bilobed at the lower margin; anther cap ovoid in outline, 2.0-2.2 mm long, apex obtuse; pollinia 2, soft and mealy, without caudicles. Pedicel with ovary slightly bent upwards or downwards, 18.5-23.5 mm long, ca. 2 mm in diameter, dark purple, pubescent, bearing sparse glandular hairs. Capsules (immature) pendulous, claviform or fusiform, 5.5-6.5 cm long, 0.7-1.1 cm diameter. Seeds not seen.

Additional specimens examined (paratypes).

Thailand. Songkla Province : Ton Nga Chang Wildlife Sanctuary, ca. 100 m, 06°59'43.91"N, 100°09'00.57"E, 22 October 2017, S. Chantanaorrapint & A. Chantanaorrapint 2810 (PSU), 16 November 2018, S. Chantanaorrapint & O. Suwanmala 2732 (PSU); Ban Yang Ko Community Forest, 7 December 2021, C. Leeratiwong 21-1752 (PSU) .

Phenology.

Flowering and fruiting observed from October to December.

Distribution, habitat and ecology.

Aphyllorchis periactinantha is known only from two localities in Songkhla province (Fig. 1 ); however, it may also occur in other areas in southern Thailand with a similar vegetation type. The new species was found growing amongst leaf litter, in shade in lowland broad-leaf forest dominated by dipterocarps such as Anisoptera costata Korth., Dipterocarpus kerrii King, Hopea ferrea Laness., H. odorata Roxb., and Shorea gratissima (Wall. ex Kurz) Dyer, ca. 100 m above sea level. During the field surveys, we found a stingless bee ( Tetragonula sp.) visiting the flower (Fig. 3D ). However, its status as a pollinator could not be confirmed.

Etymology.

Greek prefix peri -, about, actis, ray or radiate, and anthos, flower, alluding to subactinomorphic flowers.

Conservation status.

This species is currently known from two subpopulations, representing two locations, which are in protected areas (Wildlife Sanctuary and community forest). One of the subpopulations is located beside a waterfall, which is a common visiting site for tourists. Therefore, habitat quality is threatened by trampling and other destructive activities potentially caused by regular visits by tourists to the area, namely the attraction of wild boars. Together, these have the potential to cause a population reduction. The other subpopulation is also somewhat disturbed by human activities such as illegal logging. Moreover, the number of mature individuals observed is fewer than 50. The extent of occurrence cannot be estimated because the species is known only from two subpopulations and its area of occupancy is estimated to be only 8 km2. Aphyllorchis periactinantha is, therefore, assigned a preliminary status of Critically Endangered based on subcriterion C2a(i).

Figures

Figure 1. Distribution of Aphyllorchis periactinantha A. Chantanaorr. & Chantanaorr. (black circle) in Thailand.

Figure 2. Aphyllorchis periactinantha A. Chantanaorr. & Chantanaorr. A flower, lateral view B flower, top view C floral bract D column and labellum, side view E dorsal sepal F, G lateral sepals H, I petals J labellum K column and anther cap in ventral view L, M anther caps. Drawn by S. Chantanaorrapint.

Figure 3. Aphyllorchis periactinantha A. Chantanaorr. & Chantanaorr. in situ A habit B inflorescence C flower in front view D flower in oblique view with stingless bee (Tetragonula sp.) E column in ventral view F immature fruits G rhizome and roots A-E, G photographed by S. Chantanaorrapint F by C. Leeratiwong.