Clerodendrum angustipetalum Satthaphorn, A.J.Paton & Leerat., 2021

Satthaphorn, Jiratthi, Paton, Alan J. & Leeratiwong, Charan, 2021, Clerodendrum angustipetalum, a new species of Clerodendrum (Lamiaceae) from Thailand, Phytotaxa 491 (2), pp. 177-183 : 178-182

publication ID	https://doi.org/ 10.11646/phytotaxa.491.2.7
persistent identifier	https://treatment.plazi.org/id/E7359513-9252-FFC6-07BA-E7B5FECCFEB5
treatment provided by	Marcus
scientific name	Clerodendrum angustipetalum Satthaphorn, A.J.Paton & Leerat.
status	sp. nov.

Treatment

Clerodendrum angustipetalum Satthaphorn, A.J.Paton & Leerat. View in CoL , sp. nov. ( Fig. 1 View FIGURE 1 , 2 View FIGURE 2 ).

This new species belongs to section Clerodendrum and is most similar vegetative and inflorescence characters to C. nutans Wall. ex Jack (1820: 17) , whereas they mainly differ from that species in subcoriaceous leaf texture (vs membranaceous in C. nutans ) with 3.62–9.16 leaf ratio (length/width) (vs 1.73–5.10); calyx tube 3–4 mm long (as opposed to 1–2 mm); calyx lobes 7–8 mm long (as opposed to 4–6 mm); corolla tube 16–18 mm long (as opposed to 9–13 mm); corolla lobe 17–22 by 2.8–4 mm (as opposed to 10–14 by 6.5–10 mm); stamens 4.4–4.7 cm long (as opposed to 2.5–4 cm) (see Table 1).

Type: — THAILAND. Narathiwat, Waeng, Sirinthorn Waterfall, Hala-Bala Wildlife Sanctuary , elev. 440 m , 25

May 2010, Leeratiwong 10-378 (holotype PSU!) .

Description: —Shrub 2–3 m tall. Stems more or less quadrangular, lenticellate, glabrous, light brown. Leaves simple, opposite, narrowly oblong to elliptic or oblong-elliptic, 7.5–33 by 3–7.5 cm, ratio (length/width) 3.62–9.16, apex acute or acuminate, base cuneate, upper surface dark green, margin entire or slightly undulate, glabrous, lower surface light green, subcoriaceous; lateral veins 6–10 pairs; petiole 1–4.5 cm long, adaxially grooved, slender. Inflorescences elongate, thyrsoid, terminal, pendulous, 15–30 cm long, glabrous; peduncle 6–15 cm long, grooved; pairs of compound cymes opposite or sub-opposite in the distal half of axis; lower bracts subtending cymes, leafy to linear, 6–10 mm long; axillary peduncles bearing cyme 1–3.5 cm long; upper bracts linear 2–3 mm long; cymes 3–7-flowered; bracteoles linear, up to 1 mm long, at base of pedicels or cyme branches, pedicels 1.5–3 cm long. Calyx 5-lobed, campanulate, green to greenish-red, glabrous; tube 3–4 mm long; lobes narrowly triangular, 7–8 by 1.7–2 mm. Corolla white to creamy-white, slightly pubescent; tube 16–18 mm long; lobes narrowly oblong-obovate, 17–22 by 2.8–4 mm. Stamens 4.4–4.7 cm long, base of filament slightly pubescent; anthers oblong, 3–3.2 by 1.2–1.6 mm, basifixed, yellow. Ovary oblong-subglobose; style 3.5–4 cm long; stigma bilobed, divided by ca. 0.5 mm long, terminal. Fruits not seen.

Distributions and Ecology: — C. angustipetalum is only known from Narathiwat province of southern Thailand located bordering to Malaysia ( Fig 3). The new species was found in evergreen forest under shade on moist and humus rich soil, alt. 440 m.

Phenology: —Flowering from January to May. Fruiting not seen.

Local names: —Ra ya kaew bala (ระย้าแก้วบาลา).

Etymology: —The specific epithet ‘ angustipetalum ’ refers to the narrow corolla lobes.

IUCN conservation status: —The species is only found in lowland evergreen forest of Hala-Bala Wildlife Sanctuary, Narathiwat province as an endemism and has a small population size with few (<50) individuals found by observation in the natural habitat (area of occupancy <10 km 2). Although the species was formerly collected from the well-protected forest, the location of collected is also nearby buildings. This may affect the area of occupancy of the species because of the expansion of the utilized areas. We have assessed the species as Critically Endangered (CR, B2a + b(ii, iii)+C2ai+D) according to the IUCN Red List Criteria Version 3.1 ( IUCN 2012).

Specimens examined: — THAILAND. Songkhla: Chai Khuan village (cultivated), Sadao , 20 May 2011, Leeratiwong 11-379 ( PSU) . Narathiwat: Waeng, Sirinthorn Waterfall, Hala-Bala Wildlife Sanctuary , elev. 440 m, 25 May 2010, Leeratiwong 10-378 ( PSU) .

Taxonomic note: —The new species is morphologically most similar C. nutans in its vegetative features and pendulous inflorescence, but differs mainly in calyx and corolla characters summarized in Table 1 and Fig. 4 View FIGURE 4 . Moreover, this new species is only found in southern Thailand in Narathiwat province as endemism to this area, while C. nutans naturally occurs in northern, south-western, central, eastern and peninsular Thailand including India, Myanmar, Vietnam and Indonesia ( Leeratiwong et al. 2011, Wearn et al. 2019). Other two species, C. disparifolium Blume (1826: 809) and C. laevifolium Blume (1826: 808) , are frequently confused with C. nutans in the Malesian region ( Wearn & Mabberley 2011). However, C. laevifolium differs in having subsessile leaves and broader calyx lobes, whereas C. disparifolium has a more erect inflorescence with yellow flowers distributed along the inflorescence.

Two sheets, Leeratiwong 11-379, were also found in PSU herbarium, collected in 2011 from Chai Khuan village, Sadao, Songkhla province. This specimen was labelled as a part of a cultivated branch growing in rubber plantation. It was originally taken from the same individual in Hala-Bala Wildlife Sanctuary to be an ornamental plant in this area.

In addition to the previous work of Leeratiwong et al. (2011), there are now 4 known species of Clerodendrum found natively in southern Thailand with pendulous inflorescences. An updated identification key of these species is presented below.