Dischidia phuphanensis Chatan & Promprom, 2020

Promprom, Wilawan & Chatan, Wannachai, 2020, A new species of Dischidia (Apocynaceae, Asclepiadoideae) from North-eastern Thailand, PhytoKeys 144, pp. 23-30 : 23

Dischidia phuphanensis Chatan & Promprom sp. nov. Figures 1 , 2

Diagnosis.

Dischidia phuphanensis is most similar to D. tonkinensis , but the new species differs from the latter in its elliptic or narrowly elliptic or slightly oblanceolate leaves (leaves in D. tonkinensis are ovate to ovate elliptic, rarely obovate), apex of corona lobes obtuse (with tips pointing downward in D. tonkinensis ), yellow base of the corolla tube and light yellow or white apices of the lobes (white or orange-yellow corolla tube and lobes in D. tonkinensis ) and the absence of a corolline corona (corolline corona present in D. tonkinensis ). (Figures 1 , 2 )

Type.

Thailand: Sakon Nakhon Province, Phu Pha Yol National Park, 300-400 m, 16°56.126667'N, 104°2.336667'E, 7 August 2017, W. Chatan 2489 (holotype: BKF!; isotype: BK!).

Description.

Plant epiphytic or lithophytic, sometimes pendulous, fleshy, growing loosely rooted on the host trees or shrubs or on rocks, glabrous except in tube of corolla. Branches terete, 2.0-2.5 mm thick, green or greenish-purple; internodes 5-15 cm long. Stipular colleters paired, triangular, ca. 0.1 mm long. Leaves with cylindrical (slightly flattened above), 7-13 × 2.0-2.3 mm petiole; lamina green, dark green or purplish-green, underneath lighter green, slightly fleshy and coriaceous, elliptic, narrowly elliptic or slightly oblanceolate, 3-5 × 1.5-2.0 cm, apex acute-apiculate, base round or slightly acute, margin entire, gland present on adaxial side near lamina base, midrib and secondary veins inconspicuous on both surfaces. Inflorescences umbelliform, usually bearing 1-4 open flowers and 2-5 developing buds; bracts 2 subtending each flower, triangular, ca. 0.5 × 0.5 mm, greenish-brown, apex acute; peduncle extra-axillary or apparently axillary, persistent, 0-3 mm long; rachis 1-5 per peduncle, bearing scars of previous flowerings 1-3 × 1.0-1.8 mm; pedicels 1-2 × ± 0.5 mm. Sepals greenish-white, lobes ovate, 0.6-0.8 × 0.5-0.8 mm, apex round, without colleters. Corolla broadly urceolate or slightly globose, 2.4-2.6 × 2.4-2.5 mm, basally yellow, progressively fading into light yellow or white at the tips of the lobe, corolla tube with one ring of retrorse hairs in throat; lobes triangular to deltate, light yellow or white, 1.3-1.5 × ca. 1.3 mm, apex acute; corolline corona absent. Gynostegium conical in outline, 1.8-2.0 mm tall, 1.4-1.6 mm in diameter. subsessile; stipe ca. 0.1 mm tall. Staminal corona lobes anchor-shaped, stalk ca. 0.8 mm high, apical part ca. 0.6 × 0.8 mm, apex obtuse. Pollinarium erect, ca. 2 mm long. Pollinium yellow, 0.6-0.8 × 0.20-0.22 mm, ellipsoidal; translator arms 1.0-1.2 mm long; corpusculum ovate, reddish-brown, 0.15-0.16 × 0.05-0.07 mm. Ovary bicarpellate, bottle-shaped and slightly flattened, 0.7-1.0 mm long, each carpel ca. 0.2-0.5 mm in basal diameter. Follicles solitary by abortion. linear, 38-45 × 2.5-3.0 mm, green when immature changing to brown when ripe. Seed slightly cylindrical, 3.8-4.0 × 1.3-1.5 mm, base obconic, bearing white coma 30-32 mm long.

Additional specimen examined.

Thailand, Sakon Nakhon Province: Phu Pha Yol National Park, 300-400 m alt., 16°56'07.2"N, 104°02'21.1"E, 5 September 2017, W. Chatan 2904 (paratype: BKF).

Phenology.

Flowering in July-September and fruiting in Aug-December.

Distribution.

The new species is endemic to Thailand and is known only from the type locality, Phu Pha Yol National Park, Sakon Nakhon Province, north-eastern Thailand (Figure 3 ).

Ecology.

This new species grows in both slightly open and in shaded areas in mixed deciduous forest at an elevation of 300-400 m.

Vernacular name.

Thao Rag Noi.

Etymology.

The specific epithet of Dischidia phuphanensis refers to its type locality, the Phuphan mountain range.

Preliminary conservation status.

One population of Dischidia phuphanensis was found at the type locality in Phu Pha Yol National Park, Sakon Nakhon Province, north-east Thailand. It is estimated to number fewer than 250 mature individuals. Therefore, it should be considered as "Endangered (EN)" according to the IUCN criteria D ( IUCN 2017).

Discussion.

Dischidia phuphanensis is similar to D. tonkinensis , from China, Indochina and Thailand ( Thaithong et al. 2018). Similarities include their stems (thick, succulent, 2-3 mm in diameter, glabrous), glabrous petiole and lamina, succulent and coriaceous leaves and their glabrous corolla lobes. However, the new species differs from D. tonkinensis in its elliptic or narrowly elliptic or slightly oblanceolate leaves, the obtuse apex of the staminal corona lobes, the yellow base of the corolla tube, the light yellow or white apices of the lobes and absence of a corolline corona. Dischidia tonkinensis has ovate to ovate-elliptic, or rarely obovate lamina, the apices of the staminal corona lobes are retuse; it has a white or orange-yellow corolla tube and lobes and possesses a corolline corona. The new species is similar to D. acuminata Costantin, from Vietnam, in that they share the 1-5 branches to the inflorescence, the short peduncle 0-3 mm long and the absence of a corolline corona. It differs from D. acuminata by the triangular to deltate corolla lobes and with acute apices (narrowly shape, thick and abaxial side nose-like in D. acuminata ( Constantin 1912))

The genus Dischidia may be divided into two main groups based on the leaf types, i.e. those with pitcher-like leaves and species with non-pitcher-like leaves. Dischidia phuphanensis has non-pitcher-like leaves. The most recent revision of Dischidia in Thailand was by Thaithong et al. (2018) and nineteen species were recognised. This was made up of one species with pitcher-like leaves and 18 species with non-pitcher-like leaves. After this new species is added to this group, the number of species with non-pitcher-like leaves is 19. A key to the species with non-pitcher-like leaves in Thailand is provided below and is modified from Thaithong et al. (2018). Details of the morphological differences between D. phuphanensis and D. tonkinensis are presented in Table 1 .

Key to species of Dischidia with non-pitcher-like leaves in Thailand

Figures

Figure 1. Dischidia phuphanensis. A Plant climbing on rock B plant climbing on branches of shrub 2 - 3 m tall C branches and leaves D inflorescence E follicle (nearly mature) F dehiscent follicle. Photographed by Wannachai Chatan from W. Chatan 2489 (A-D) and W. Chatan 2904 (E, F).

Figure 2. Dischidia phuphanensis. A Branch with leaves and inflorescences B bud C flower D dissected flower with half of corolla removed E calyx from abaxial side F gynostegium (side view), with coronal lobes removed G gynostegium (from above) H pollinarium I pistil J pistil (style-head removed) K follicle L seed A-J drawn by Wannachai Chatan from W. Chatan 2489, and K, L from W. Chatan 2904.

Figure 3. Distribution of Dischidia phuphanensis (black triangle) in Phu Pha Yol National Park, Sakon Nakhon Province, Thailand.