Toxocarpus incarnatus A. Kidyoo, 2022

Kidyoo, Aroonrat, 2022, Toxocarpus incarnatus (Apocynaceae, Secamonoideae), a new species from Thailand, Phytotaxa 564 (1), pp. 133-138 : 134-137

Toxocarpus incarnatus A. Kidyoo sp. nov. ( Figs. 1 ‒3)

Type: — THAILAND. Ratchaburi province: Suan Phung , 600‒650 m elevation, 3 August 2019, A. Kidyoo 66 (holotype BKF!, isotype BCU!) .

Toxocarpus incarnatus is close to T. oblanceolatus Kerr (1938: 450) , being similar in having rusty pubescent young branches and inflorescences, large leaves (> 9 cm long), inflorescences that are shorter than leaves and bear sub-rotate flowers, each flower with corolla tube covered with trichomes inside, coronal scales that are slightly longer than anthers, short stout style-head (<1.4 mm long) whose tip is obtuse to slightly retuse. The former is, however, clearly distinguished by its ovate-oblong to elliptic-oblong leaves, bright pink-orange flowers, and style-head rising up to less than half the length of the corolla tube. The latter, on the other hand, has obovate to oblanceolate leaves, white flowers, and a style-head that rising up to the throat of the corolla tube.

Twining climber, with milky exudate in all vegetative parts, young parts covered with rusty red soft trichomes. Stem and branches terete, 2–10 m long, 2–5 mm in diameter, rusty pubescent, green to pale greenish brown when young, turning brown and with numerous lenticels later. Leaves opposite; petiole sub-terete, 0.6‒1.1 cm long, 2‒2.5 mm in diameter, rusty pubescent; blade coriaceous, ovate, elliptic, ovate-oblong to elliptic-oblong, 10‒15 × 4‒5.5 cm, base cuneate to obtuse, apex acute or obtuse with a small mucro, margins entire; adaxial surface green to dark green, glabrescent to pubescent, trichomes grey or white to brownish white; abaxial surface pale green, glabrescent to rusty pubescent; midrib greenish white, prominently convex and covered with rusty trichomes abaxially; lateral veins slightly visible on both surfaces, 6‒8 on each side, at acute angle to the midrib. Inflorescences axillary to sub-axillary, shorter than leaves, many times dichotomously branched cyme, 3‒10 cm long, many flowers; peduncle 1‒2 cm long, 2‒3 mm in diameter, entirely rusty pubescent; bracts lanceolate, 3‒5 × 2‒2.5 mm, rusty pubescent outside; pedicels short, 1.5‒2.2 mm long, 1.5‒1.9 mm in diameter, rusty pubescent; bracteoles attached at base of pedicel, lanceolate, 2.5–3.4 × 1–1.3 mm, apex acute, rusty pubescent. Flower bud narrowly ovoid, apex acute. Calyx lobes lanceolate, 3.5‒3.9 × 1.3‒1.5 mm, greenish white, rusty pubescent outside, ciliate at margins, with a basal gland on the inside of each lobe sinus. Corolla salver-campanulate, ca. 1 cm in diameter, light pink outside and bright pinkish orange inside; tube slightly inflated at the middle, 5.5‒6.2 mm in length, 4.3‒4.7 mm in diameter, densely covered with long white trichomes inside; lobes overlapping to the left in bud, obliquely ovate to ovate-oblong, 6.4‒6.8 × 2.8‒3.1 mm, apex acute, glabrous on both surfaces, except white trichomes on the inside of the basal parts and rusty trichomes at tips on the outer side. Gynostegium conical-cylindrical, 2.1‒2.4 mm in length, 1.5‒1.8 mm in diameter. Coronal scales thick, yellow, shorter than style-head; each scale ovate, 1.1‒1.3 × 0.8‒1 mm, with a short triangular lobe directed outwards to either side, distal part tapering gradually towards the truncate apex. Pollinaria each with 4 pollinia; pollinium yellow, oblong-ellipsoid, 0.21–0.24 × 0.06–0.07 mm; corpusculum brown, ovate, 0.09–0.1 × 0.06–0.07 mm. Style-head ovoid to ellipsoid, 0.9–1 mm in length 0.7–0.8 mm in diameter, apex obtuse or slightly retuse, glabrous; included, rising up to less than half the length of the corolla tube. Ovary ovoid, 0.7–0.8 mm in length 0.5–0.6 mm in diameter, greenish white, glabrous. Fruits and seeds not observed.

Distribution and habitat:— Toxocarpus incarnatus occurs at about 600–650 m elevation in Ratchaburi province, Thailand. It grows in loam soil in open to semi-shady areas at the edge of the disturbed evergreen forest (with a rural road running alongside), and usually climbs up to 10 m on bamboos. In addition to the plant material collected from the type locality, another specimen of this species was collected in 1967 from the roadside thicket in Lampang province at about 350 m elevation (based on T. Shimizu et al. 10727).

Phenology:—Flowering occurs from June to August.

Etymolgy:—The specific epithet ‘ incarnatus ’ refers to the peach-coloured corolla.

Conservation status:— Toxocarpus incarnatus is known only from two localities. In Lampang, the number of mature plants is unknown, whereas 30–50 individuals were found in the degraded forest on the side of the rural road in Ratchaburi province. The latter site has suffered exploitation by local communities, including transformation of land for use in agriculture, for construction of roads, and to install buildings for tourism. Moreover, the current afforestation practice in the area using non-native plant species poses a potential risk of damaging the integrity of natural ecosystem and diversity. Following IUCN (2019), a conservation assessment of Endangered: B1ab(iii) should be assigned to this species due to its limited locations, of which at least one is evidently susceptible to threats in the near future, extent of occurrence of much smaller than 5,000 km 2, and restricted geographic distribution.

Discussion: —Considering the floral characteristics, compared with the other known species of Toxocarpus which are generally characterized by white or yellow flower with a slender conical or filiform style-head that either rises up to the throat of the corolla tube or is exerted beyond the end of the throat, T. incarnatus is clearly distinguished by its unusual bright peach-coloured corolla, tubular corolla tube that is slightly inflated at the middle, gynostegium completely included with short, stout ovoid to ellipsoid style-head that rises up to only less than half the length of the corolla tube. Moreover, T. incarnatus has rusty pubescent young branches and inflorescences, short pedicel, subdense inflorescence that is shorter than leaves, flower with corolla tube longer than calyx and nearly as long as the length of the corolla lobes. Only a few known species share these traits ( Hooker 1883; Costantin 1912; Li et al. 1995; Thaithong et al. 2018), i.e. T. concanensis Hooker in Hooker (1883: 14), T. oblanceolatus Kerr and T. spirei Costantin (1912: 51) . However, despite some traits in common, T. concanensis and T. spirei differ clearly in shape of their style-heads. That of the former is long fusiform with a slender notched tip, whereas that of the latter is constituted of disc-like lower part, subulate upper part and a deeply bifid tip. The style-head of T. oblanceolatus , like that of T. incarnatus , is short stout with an obtuse to slightly retuse tip.

Thereby, T. oblanceolatus , a species endemic to Thailand, is most similar to T. incarnatus . They are also alike in ecology, occurring in evergreen forests at the same elevation range, i.e. T. incarnatus has been found from 350 to 650 m elevation in southwestern and northern regions of Thailand and T. oblanceolatus has been found at 500 m elevation in northern region of the country. The new species can be clearly separated from T. oblanceolatus by its leaf and flower characters ( Table 1 ). Toxocarpus incarnatus has ovate or elliptic to oblong leaves, pink to orange flowers with a stylehead rising up to less than half the length of the corolla tube. By contrast, T. oblanceolatus has oblanceolate or obovate leaves, white flowers with a style-head that rises up higher, nearly to the throat of the corolla tube.

Furthermore, compared to the toxocarpoid Secamone sensu Klackenberg (2006) species from Southeast Asia described by Klackenberg (2006, 2010), T. incarnatus possesses a style-head that largely set it apart. It is characterized by a short and stout, ovoid to ellipsoid style-head that rises up to less than half the length of its corolla tube, while all those toxocarpoid Secamone species have long slender cylindric or fusiform style-heads that either rise up to the throat or markedly exserted from the corolla tube.

Additional specimen examined:— Toxocarpus incarnatus A. Kidyoo : THAILAND. Lampang province: Pang La to Huay Tak , ca. 350 m elevation, 24 September 1967, T. Shimizu et al. 10727 ( BKF, QBG) .

Figures

FIGURE 1. Toxocarpus incarnatus. A. Flowering branch. B. Abaxial surface of the leaf. C. Adaxial surface of the leaf. D. Inflorescence with a blooming flower and several flower buds, one of which being fully developed. E. Top view of flower. F. Longitudinal section of flower showing corona and gynostegium. G. Bottom view of calyx. H. Top view of calyx. I. Side view of gynostegium with corona. J. Top view of gynostegium with corona. K. Side view of gynostegium showing ovaries and style-head. L. Pollinarium. From A. Kidyoo 66. Photographs by A. Kidyoo.