Mitrephora sirindhorniae Chalermglin, Leerat. & R.M.K.Saunders, 2023

Mitrephora sirindhorniae Chalermglin, Leerat. & R.M.K.Saunders sp. nov.

Figs 4 View Figure 4 , 5 View Figure 5

Diagnosis.

Mitrephora sirindhorniae resembles M. tomentosa Hook.f. & Thomson, but is distinguished by its leaves that are sparsely hairy abaxially, larger sepals (8-10 by 10-12 mm), larger outer petals (40-60 by 22-35 mm), larger inner petals (14-16 by 14.5-15 mm), longer flowering pedicels (25-27 mm), shorter monocarp stipes (2.5-8 mm) and monocarps with a longitudinal ridge.

Types.

Thailand: TISTR Annonaceae collection plot, Khlong Luang district, Pathum Thani Province, Central Thailand, ca. 5 m alt., 30 April 2021, P. Chalermglin 640430 (originally from small sandstone hill in Bueng Kan Province, North-Eastern Thailand, ca. 200 m alt.) (holotype PSU; isotypes BKF, KKU, QBG).

Description

(from cultivated material). Small trees, to 4 m (in cultivation). Young branches densely pubescent. Leaf laminas subcoriaceous, (oblong-)lanceolate, 7-15 by 1.5-6 cm, base slightly oblique, broadly cuneate to slightly rounded, apex acute to rarely acuminate, glossy, glabrous adaxially, sparsely pubescent (denser on midrib) abaxially, secondary veins 8-12 pairs per leaf, without domatia; petioles 4-7 mm long, densely pubescent. Inflorescence rachides simple, with rachis internodes remaining short, 3-5 mm long, 2-3-flowered, densely pubescent; pedicels 25-27 mm long. Sepals free, ovate, not imbricate, 8-10 by 10-12 mm, densely pubescent abaxially, glabrous except densely pubescent at margin adaxially. Outer petals greenish-yellow, turning yellow, (broadly) oblanceolate, 40-60 by 22-35 mm, not clawed, margin undulate with age, apex acute, sparsely pubescent ab- and adaxially. Inner petals pale yellow with purple stripes apically, 14-16 by 14.5-15 mm, claw slightly incurved, densely pubescent ab- and adaxially. Stamens 1-1.5 mm long, connective truncate, glabrous. Carpels 15-20 per flower, 2-2.5 mm long; ovary oblong 1.2-1.5 mm long, sparsely pubescent, stigma club-shaped, 0.5-0.8 mm long, hairy; ovules 8-10 per carpel. Fruits with 7-14 monocarps, borne on a pedicel 20-30 mm long, 3-5 mm wide, densely pubescent. Monocarps yellow when ripe, (ellipsoid-)obovoid to ovoid, 15-30 by 10-25 mm, smooth, with longitudinal ridge, densely pubescent; stipes 2.5-8 mm long, densely pubescent. Seeds 1-10 per monocarp, semi-lenticular (lowermost and uppermost within monocarp) or discoid (others), 9-16 by 8-9.5 mm, surface glabrous, pitted.

Phenology

(in cultivation). Flowering in April and fruiting in July.

Distribution and habitat.

Endemic to Bueng Kan Province, North-Eastern Thailand (Fig. 3 View Figure 3 ). Growing on sandstone hill in dry dipterocarp forest; ca. 200 m alt.

Etymology.

Named after Her Royal Highness Maha Chakri Sirindhorn, in honour of her project on plant germplasm conservation in Thailand.

Local name.

Maha phrom sirinthon (มหาพรหมสิรินธร) (general).

Additional specimens examined

( paratypes). Thailand: Pathum Thani Province, Khlong Luang District , TISTR Annonaceae collection plot, ca. 5 m alt., 23 July 2020, P. Chalermglin 630723 (originally from small sandstone hill in Bueng Kan Province, North-Eastern Thailand, ca. 200 m alt.) (PSU).

Discussion.

Mitrephora sirindhorniae is characterised by its sparsely hairy abaxial leaf surface, flowers with long outer petals (40-60 mm) that are broadly oblanceolate, and by its densely pubescent fruits with a longitudinal ridge. The species is morphologically most similar to M. tomentosa Hook.f. & Thomson, from which it differs as its leaves are sparsely hairy abaxially ( vs densely hairy), with flowers with larger sepals (8-10 by 10-12 mm vs 5-9 by 5-9 mm), outer petals (40-60 by 22-35 mm vs 16-19[-34] by 7.5-18 mm), inner petals (14-16 by 14.5-15 mm vs 8.5-16.5 by 7-12.5 mm), and longer flowering pedicels (25-27 mm vs 11-23 mm). The monocarp stipes are shorter (2.5-8 mm vs 16.5-29[-39] mm), and the monocarps have a longitudinal ridge.