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

Leeratiwong, Charan, Chalermglin, Piya & Saunders, Richard M. K., 2023, Three new species of Mitrephora (Annonaceae) from Thailand, PhytoKeys 218, pp. 93-107 : 93

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

Figs 4 , 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 ). 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.

Figures

Figure 3. Distributions of Mitrephora langsuanensis, M. sirindhorniae and M. sukhothaiensis.

Figure 4. Mitrephora sirindhorniae sp. nov. A flowering branch B, C flowers D flower, showing calyx E flower, showing indument on adaxial surface of inner petals F fruit (slightly immature) G fruit (mature). Photos by P. Chalermglin.

Figure 5. Mitrephora sirindhorniae sp. nov. A vegetative branch B, C flowers D, E sepals (ab- and adaxial) F, G outer petals (ab- and adaxial) H, I inner petals (ab- and adaxial) J, K stamens (ab- and adaxial) L carpel M fruit, composed of separate monocarp N seeds. Drawn by A. Somphrom, A-L from P. Chalermglin 640430 (PSU), M-N from P. Chalermglin 630723 (PSU).