Maerua koratensis Srisanga & Watthana, 2021

Srisanga, Prachaya, Muangsan, Nooduan, Choopan, Thiamhathai, Thangthong, Jakrapong, Pratcharoenwanich, Ratchada & Watthana, Santi, 2021, Maerua koratensis (Capparaceae), a new species from Thailand, Phytotaxa 498 (3), pp. 213-219 : 215-218

Maerua koratensis Srisanga & Watthana , sp. nov. ( Figs. 1–2 )

Diagnosis: — Maerua koratensis is similar to M. juncea subsp. juncea in having petaliferous flowers with distinct 4-lobed laciniate disc and the same number of stamens, but it differs in the following combination of traits: subshrub with ascending shoots, ± 1.5 m tall (vs. small shrub over 2 m or climber up to 15 m tall), reddish-brown branches with white lenticels (vs. green and striate branches), simple leaves, not glaucous beneath (vs. simple or 3-foliolate leaves, often rather glaucous beneath), and narrowly cylindrical, torulose to moniliform fruit with faintly colliculate surface (vs. ellipsoidal fruit with smooth surface).

Type: — THAILAND. Nakhon Ratchasima: Sikhio District, Lat Bua Khao , elevation 260 m, 28 February 2019 (fl., fr.), Pokaew & Chanokkhun 167 (holotype: QBG!; isotypes: AAU!, BKF!, QBG!) .

Subshrub with ascending shoots, ± 1.5 m tall, unarmed. Branches slender, reddish-brown, glabrous, with white lenticels. Leaves simple, alternate, petiolate; lamina narrowly oblong-lanceolate to lanceolate, (3.5–)5–9(–11) × (0.5–)1– 2(–2.5) cm, subcoriaceous, glabrous on both surfaces; apex acute, mucronate, obtuse to retuse; margin entire; base broadly cuneate to obtuse; midrib and lateral veins flat above, raised beneath; lateral veins 5–7 pairs, distinct on both surfaces; petiole (1.5–)3.5–5(–7) mm long, glabrous, canaliculate with crenulate edges; stipules triangular, ca. 0.5 mm long. Inflorescences 2–5-flowered in terminal lax raceme, or solitary in the axils of the upper leaves. Flowers actinomorphic, pedicellate; pedicels 13–40 mm long, glabrous. Receptacle infundibular to narrowly campanulate, 3–4 mm long, 3–3.5 mm wide at mouth, with longitudinal ribs, glabrous or sparsely puberulous; disc 2.5–3 mm long, pale green, glabrous, tube ca. 1 mm long, lobes 4, 1.5–2 mm long, laciniate at apex. Sepals 4, elliptic, navicular with distinct median nerve, spreading, 15–17 × 5–6 mm (7–8 mm wide when flattened), pale green, glabrous, apex acute to shortly acuminate, margin shortly woolly. Petals 4, elliptic to obovate, clawed, 8–9 × 3–4 mm, pale greenish-white, glabrous, apex acuminate, margin slightly and irregularly crenulate towards apex. Androgynophore 2–5 mm long, glabrous, exceeding the receptacle by 1–1.5 mm. Torus ca. 2.5 mm wide. Stamens 33–38; filaments 20–22 mm long, white, glabrous; anthers oblong, subbasifixed, ca. 2.5 × 1 mm, pale green, dehiscing by longitudinal slits. Gynophore 13–17 mm long, white, glabrous. Ovary oblong-cylindrical, pale green, 4.5–5 mm long, ca. 1 mm diam., 1-locular; placentas 2, ovules up to 10; stigma capitate, green, sessile. Fruit narrowly cylindrical, torulose to moniliform, 1.5–4.5 cm long, 0.6–1.1 cm diam., yellow when mature, faintly colliculate, glabrous, indehiscent. Seeds 1–7, reniform, 6.5–8 mm long, black, covered with pulp.

Phenology: —Flowering: January–March; fruiting: February–April.

Distribution and habitat: — Maerua koratensis is only known from Nakhon Ratchasima Province in Thailand ( Fig. 3 ).

Vernacular name: —Jaeng suranaree (Thai).

Conservation status: —This species has been collected from five subpopulations. Only three subpopulations can be locally accessed but the old collections of 1931 and 1967 do not have enough information to search where the subpopulations are. So far only 14 individuals without any seedling have been found in the disturbed area with Cassava crop. Accordingly, the species would fall into the IUCN category of Critically Endangered, CR C2a(i, ii); D ( IUCN Standards and Petitions Committee 2019).

Etymology: —The specific epithet refers to “Korat” which is commonly used as an alternative name for Nakhon Ratchasima Province, the type locality of the new species.

Additional specimens examined (paratypes): — Thailand: Nakhon Ratchasima (Korat); Sikhio, ca. 200 m, 20 January 1931 (fl.), A . F .G. Kerr 20402 ( BK!); Sikhio , ca. 200 m, February 1967 (fl.) C . Chermsirivathana s.n. ( BK!); Sikhio, Kritsana, ca. 260 m, 31 March 2019 (fl., fr.), Pokaew & Chanokkhun 168 ( BKF!, QBG!); Dan Khun Thot , ca. 280 m, 20 January 2019 (fl.), T . Choopan 2019-015 ( BKF!, QBG!) .

Notes: — Maerua koratensis is similar to M. juncea subsp. juncea in having petaliferous flowers with distinct 4- lobed laciniate disc and a similar number of stamens ( Killick 1969, Abreu et al. 2014, Hyde et al. 2019, PROTA4U 2019), but can be distinguished as outlined in the diagnosis and Table 1.

Maerua koratensis is only known from a restricted locality in Nakhon Ratchasima Province, Thailand, South-East Asia whereas M. juncea subsp. juncea is confined to tropical East Africa: Tanzania, Malawi, Mozambique, Zambia and Zimbabwe, and tropical South Africa: Botswana, Namibia and Swaziland.

Figures

FIGURE 1. Maerua koratensis in its natural habitat.A. Flowering branches. B. Fruiting branches.

FIGURE 2. Maerua koratensis. A. Flowering branch showing flower buds, opened flowers and fully mature flowers. B. Single flower with sepals, petals and the majority of stamens removed; the stamens are situated on a torus elevated on an androgynophore which is concealed by a receptacle. C. Petals; left ventral side and right dorsal side. D. Sepals, left ventral side and right dorsal side. E. Receptacle. F. Fruits.

FIGURE 3. Known distribution of Maerua koratensis.