Memecylon rostratum Thwaites

Perera, Amila, Jayasinghe, Himesh, Gopallawa, Bhathiya, Madawala, Isuru, Gunatilleke, Nimal & Geekiyanage, Nalaka, 2025, Reinstatement of Memecylon elegantulum (Melastomataceae) and recircumscription of Memecylon rostratum, two species endemic to Sri Lanka, PhytoKeys 259, pp. 67-80 : 67-80

Memecylon rostratum Thwaites , Enum. Pl. Zeyl. 111 (1859); Trimen, Handb. Fl. Ceylon, 2: 218 (1894); K. Bremer, Opera. Bot. 50: 21 (1979), p. p.; K. Bremer in Dassan., Revis. Handb. Fl. Ceylon 6: 224 (1987), p. p.

Figs 4 , 5

Type. •

Sri Lanka n. l., n. d., n. coll., C. P. 1560 (lectotype: the largest branch with flowers [second from the left] of PDA [ PDA 00002923 !], designated here)

Description.

A small tree, to 8 m tall; outer bark smooth, not longitudinally striate, yellowish brown; young branchlets terete; flush leaves pale yellowish green, sometimes with a red tinge; internode distance 15–30 mm. Leaves green above, paler below, lustrous on both sides in live state, brown on upper side and yellow-brown on underside in dried state; petiole 2–5 mm long; lamina subcoriaceous, elliptic to ovate 40–70 × 25–38 mm, caudate to acuminate, obtuse to rounded at extreme apex, broadly to narrowly cuneate at base, margins flat, rarely slightly revolute towards base; midrib adaxially slightly grooved, abaxially obscurely raised; lateral veins 7–9 pairs, invisible in live state, hardly visible abaxially in dried state; intramarginal vein 0.3–0.5 mm from the margin. Inflorescence 1 (– 2) per node, axillary, mainly on nodes below the existing leaves and extending in to the lower leaf nodes; peduncle often unbranched, (0 –) 2.5–5 mm long, thick, obscurely quadrangular to terete, green; secondary axils almost sessile when the peduncle is branched; flowers umbellate, 3–14 flowers per inflorescence; minute bracts at the base of the petiole early caducous, brown. Flowers pedicel 0.4–1 cm long, white; hypantho-calyx broadly infundibuliform to pyriform with an abrupt medial inflation, 1.3–1.5 mm long, 1.8–2.3 mm wide, outside smooth, white; calyx lobes 4, 0.4–0.5 mm long, 1.2–1.4 mm wide, obtuse to acute at apex; epigynous chamber smooth, without any furrows; exposed petals dome-shaped with an apiculate apex and 4 grooves radiating from the centre of each calyx lobe, white at anthesis, reflexed, 1.5–2 mm long, 1.2–1.6 mm wide; filaments 2.6–3.0 mm long, purple-blue; anther connective, curved, 1.2–1.3 mm long, 0.4–0.6 mm wide, purple-blue; with a prominent red gland; anthers pale brownish yellow; style 3.5–3.8 mm, grey. Fruits 1–5 (– 7) per inflorescence, reducing in number at maturity, on stiff pedicels up to 1–4 mm; depressed globose to oblate, 6–8 × 3–6 mm diameter, topped by a persistent calycinal crown; surface smooth, white at immature stage, indigo-blue at partial maturity, then turning to blackish purple at maturity; cotyledons hardly wrinkled.

Distribution and habitat.

Southwestern lowland rainforests of Sri Lanka except the coastal zone, in the elevation range 200 - – 500 m (Fig. 3 ). PDA 00002921 ! sheet contains information on three localities in Kandy District (the specimens were mounted by Thwaites in the 1800 s). No further collections have been reported from natural habitats in the surroundings other than from the trees planted at the Royal Botanical Gardens, Peradeniya. It is thus possible that this historical gathering information may not relate to this species. Memecylon rostratum is usually confined to the upper level of the rainforest understorey, often on ridges within a given topography.

Phenology.

The main flowering season was reported from March to May, with fruits produced from May to August. A second season produces flowers from September to November, with fruits in December to February.

Notes.

Trimen (1894) mentioned that flowers of Memecylon rostratum are very pale blue, while Alston (1931), in his key to the species, repeated the same. The protologue mentioned that the petals were white. This was not necessarily a misconception: the petals are white while the inside of the hypanthocalyx and anther connectives are pale blue in this species. This is evident also from the drawing curated at PDA, which was based on syntypes.

Bremer (1979) lectotypified the name as ‘ C. P. 1560 PDA ’ while considering C. P. 1560 in BM, K & US as iso-lectotypes. We found that C. P. 1560 at PDA consisting of two herbarium sheets. PDA 00002923 ! contains four branchlets with some detached leaves and carries no information about the gathering. PDA 00002921 ! contains 6 branchlet fragments, one of which retains three attached leaves; the others lack leaves, though the detached leaves are pasted separately. The branchlet with the leaves has immature flower buds, while another branchlet that lacks leaves too, bears some young flower buds. An indistinct pencil notation on this sheet contains information on three gatherings (Hantana, Gardner; Deltota, in flower; Meda Mahanuwara, July 1852), though this cannot be explicitly assigned to the branchlets glued onto the sheet. In any event, because it is composed of multiple gatherings, Bremer’s lectotypification is incorrect. The present lectotype designation rectifies that deficiency and thereby stabilizes the identity of this species. As in the previous species, we refrain from considering other C. P. 1560 specimens as iso-lectotypes. Further, we have not included the C. P. 1560 specimens accessioned in herbaria outside Sri Lanka under the ‘ specimens examined’, pending the availability of magnified images of the flowers, and since we have encountered similar looking but evidently undescribed species in the field.

Bremer (1979, 1987) quoted Waas 509 ( PDA, US) under this species, which is a species of Eugenia [probably E. mooniana Wight ] ( Myrtaceae ). The specimens associated with C. P. 2684 and NBK 315 quoted in these publications ( Bremer 1979, 1987) belong to M. elegantulum . The specimens cited as Waas & Peeris 551 and Cramer 3720 do not exhibit sufficient detail to recognize them explicitly as Memecylon rostratum .

Specimens examined.

• Sri Lanka: Kandy District: Peradeniya , n. d., F. Fagerlind 4595 ( E 01411685 ; US 2955736 ) ; • Royal Botanic Garden, Peradeniya , 10 iii 1979, Kostermans 27421 ( L.2545523 , BR 0000030741959 , PDA [2 sheets]) ; • ibid., 25 v 1980, Kostermans 28473 ( L.2545522 ) ; • ibid., 13 ii 1904, C. C. Hosseus 12 ( M 0168532 ) ; • ibid., 2022 ix 16, H. Jayasinghe HDJ 1693 ( PDA) ; • ibid., 1964 v 26, D. Amaratunga 818 ( PDA) ; • ibid., 1955 v 30, T. B. Worthington 6746 ( PDA Ratnapura District: Sinharaja forest, between Heend Dola & Gallen Dola , 1989 iv 26, A. H. M. Jayasuriya & S. Balasubramaniam 4697 ( PDA) ; • Mulawella trail, Sinharaja , 2023 v 03, H. Jayasinghe & D. Samarasinghe HDJ 2197 ( PDA) ; Walankanda , 2 v 1976, S. Waas 1557 ( E 01411686 , L.2545521 , PDA [2 sheets]) • Kalutara District: East Kalugala Forest , 1 v 1976, S. Waas 1534 ( E 01411684 , L.2545520 , PDA [2 sheets]) • Galle District: Kanneliya forest near Hiniduma , 7 vi 1973, Kostermans 24727 ( L.2545524 , US 2955733 ) ; • ibid., 25 vii 1976, A. H. M. Jayasuriya & A. J. Kostermans 2371 ( P 05255614 , PDA) ; • Kalubowitiyana , 2023 xi 06, H. Jayasinghe, D. Dhanushka, S. Kanishka & D. Samarasinghe HDJ 2557 ( PDA) ; • Opatha , 2024 v 05, H. Jayasinghe, D. Samarasinghe, A. Perera, P. Jayasundara HDJ 3061 ( PDA) .

Figures

Figure 3. Distribution map Memecylon elegantulum Thwaites and M. rostratum Thwaites.

Figure 4. Memecylon rostratum Thwaites; A. Habit; B. Outer bark; C. Lamina upper side; D. Lamina under side; E. Flush leaves; F. Dorsal view of the inflorescence; G. Lateral view of the inflorescence; H. Dorsal view of epigynous chamber after anthesis; J. Dorsal view of the flower; K. Partially mature fruit; L. Immature fruits; M. Partially mature fruit and undeveloped fruits; N. Lateral view of flower immediately after anthesis; P. Cross-section of a partially mature fruit; Q. Longitudinal section of a partially mature fruit.

Figure 5. Line drawing of Memecylon rostratum Thwaites; A. Branch with immature fruits; B. Lamina upper side; C. Lamina under side; D. Dorsal view of flower; E. Lateral view of the flower just after anthesis; F. Dorsal view of the flower; G. Dorsal view of epigynous chamber after anthesis; H. Partially mature fruit; J. Longitudinal section of a partially mature fruit.