Memecylon elegantulum 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 elegantulum Thwaites , Enum. Pl. Zeyl. 112 (1859); Trimen, Handb. Fl. Ceylon, 2: 214 (1894)

Figs 1 , 2

Memecylon rostratum auct. non Thwaites, K. Bremer, Opera. Bot. 50: 21 (1979), p. p.; K. Bremer in Dassan., Revis. Handb. Fl. Ceylon 6: 224 (1987), p. p.

Type.

• Sri Lanka n. l., n. d., n. coll., C. P. 2684 (lectotype: third branch from the left of PDA [ PDA 00002924 !], designated here) ; Samanala Watta side of Pettigala Forest Reserve, 17 iv 2023, H. Jayasinghe et al. HDJ 2097 (epitype: PDA 00109496 , designated here) .

Description.

Memecylon elegantulum is distinguished from M. rostratum upto 2 m tall (vs treelet, to 7 m); having flush leaves deep purple-red to light pink (vs whitish green); branched, pedicellate inflorescence with 1–2 flowers (vs unbranched inflorescence with 6–9 capitate flowers); petals in bud conical with an apiculate tip (vs obtuse tip); anthers and anther connectives white (vs purplish-blue); straight anther connective without a gland (vs arched anther connective, with a prominent red gland); and fruit hanging, pale green in immature stage (vs erect, white).

Shrubs or treelets up to 2 m height; outer bark shallowly and longitudinally striate; young branchlets obscurely quadrangular, becoming terete with age; flush leaves deep purple-red to light pink; internode distance 18–25 mm. Leaves green above, much paler below, lustrous on both sides in live state, greenish-brown in dried state; petiole 1–2 mm long; lamina subcoriaceous, broadly to (rarely) narrowly elliptic, 40–65 × 15–20 mm, caudate to acuminate, obtuse at apex, narrowly obtuse to cuneate at base, margins slightly revolute toward base, slightly thickened; midrib slightly grooved adaxially, obscurely raised abaxially; lateral veins 7–9 pairs, with a few intermediaries, straight throughout, unicolorous in live state, venation visible on both sides in dried state; intramarginal vein 0.3–1 mm from the margin. Inflorescence 1 (– 2) per node, axillary on lower leaf nodes or rarely below the existing leaf nodes; main axis of the peduncle 2.5–3.5 mm long, filamentous, quadrangular, pale yellowish green, topped by (1 –) 2 capitate secondary axils, surrounded by minute bracts at the joint; secondary axils 2–3 mm long, filamentous, cylindrical, pale greenish white, topped by 2, minute, whitish bracts, holding a single flower. Flowers pedicel 4.5–5 mm long, white; hypantho-calyx broadly pyriform to infundibuliform, 1.7–1.9 mm long, 2.3–2.5 mm wide, outside smooth, white, sometimes with a bluish tinge at apex; calyx lobes 4, minute, obtuse to acute at apex; epigynous chamber smooth, without any furrows; exposed petals conical with a pointed apex in bud, white at anthesis, reflexed, 2.4–2.6 mm long, 1.8–2.1 mm wide; filaments 3.4–3.7 mm long, white; anther connective straight, 2.2–2.7 mm long, 0.6–0.7 mm wide, white; without a gland; anthers white; style 5.9–6.1 mm, white. Fruits 1–2 per inflorescence with an elongate, hanging pedicel up to 7–8 mm; subglobose, 9.5–11 × 7.5–9 mm diameter, topped by a persistent calycinal crown; surface smooth, yellowish green during immature stage, purplish blue at partial maturity, then turning blackish purple at maturity; cotyledons wrinkled.

Distribution and habitat.

Lowland rainforests of Sri Lanka, northwards to Sinharaja Forest in the elevation range 250–800 m (Fig. 3 ). It usually occurs at the lower level of the rainforest understorey, on ridges and as well as in valleys.

Phenology.

Flowering and fruiting were recorded twice a year, from February to April and from August to November.

Notes.

In the protologue of Memecylon elegantulum, Thwaites (1859) briefly described its inflorescence, flower and the fruit. All the morphological features and distribution details he provided, except the description of the pedicel, are consistent with our own observations. Thwaites mentioned, however, that the pedicel was ‘ as half as long as the calyx [calyce dimidio longioribus], while the taxon described here has pedicels approximately three times long as the calyx. Later, Trimen (1894) described the flower as sessile, which was repeated by Alston (1931). After a thorough search in herbaria, we encountered four syntypes. Although Trimen (1894) and Alston (1931) detailed the flower and the fruit, the syntypes we examined contained neither flowers nor fruits except for the crushed parts of a fruit in the pocket of BM 000944509 ! and an immature fruit in the pocket of PDA 00002922 !. Although Trimen (1894), in his enumeration, mentioned that he had only scant material of this taxon, we were unable to locate any material other than the mentioned syntypes prior to Trimen’s time.

The drawing made from C. P. 2684 by H. de Alwis, Thwaites’ draftsman ( Pethiyagoda 2007) curated at PDA, is a leafy branch with a single hanging fruit, which is bluish purple. This species has the longest pedicel (relative to the length of the hypanthocalyx) among the Sri Lankan species of Memecylon , while having a unique inflorescence architecture. Given that Thwaites noted that inflorescence was ‘ sparsely racemose’ [parce ramosis], it is possible that he was misled by this feature, thinking that the pedicel was a secondary axis of the inflorescence. The second branch from the left of PDA 00002924 ! has two broken primary axils of inflorescences, highlighting its filamentous nature. The third branch from the left of PDA 00002924 ! has a single broken inflorescence axis, including a part of the secondary axis. This inflorescence section features the bracts at the inflorescence branching.

Since little Sri Lankan material was available to him, Bremer (1979) provisionally synonymized Memecylon elegantulum under M. rostratum . Bremer (1979) lectotypified the name as ‘ C. P. 2684 in PDA ’ while considering C. P. 2684 in BM & K to be iso-lectotypes. We note, however, that there are two sheets labelled C. P. 2684 in PDA, both of poor quality. As detailed by Jayasinghe et al. (2022), a single C. P. number often included multiple gatherings. PDA 00002922 ! has an indistinct pencil notation about the gathering information (possibly ‘ Gilimale, March 1853 ’) while PDA 00002924 ! lacks any such information. This suggests that these specimens may have been the result of multiple gatherings. It is important, however, that type specimens be from a single gathering (see Article 8.2, footnote 1). Here under Art. 9.3, newly lectotypify the name, selecting the specimen in the best condition. Since the syntpes represent multiple gatherings, they are retained as such, without considering them for iso-lectotypification. Given that all the syntypes currently lack flowers as well as a complete peduncle, they only partially represent the taxon. Hence, we designate a flowering specimen as an epitype (Article 9.9).

Specimens examined.

Sri Lanka: • Ratnapura District: Kalawana , 30 iv 1970, N. Balakrishnan NBK 315 ( PDA, US 02955738 ) ; Approximately 2 miles from Rassagala , 09 xi 1975, S. H. Sohmer & S. Waas 10491 ( PDA) ; • Bambarabotuwa Forest Reserve , 15 v 2018, M. Gunathilake, N. Gunawardena & A. Sumanadasa NBS / 2018 / BAM / 071 ( PDA) ; • ibid., 14 v 2018, M. Gunathilake, N. Gunawardena & A. Sumanadasa NBS / 2018 / BAM / 023 ( PDA) ; • ibid., NBS / 2018 / BAM / 013 ( PDA) ; • ibid., 06 xi 2018, B. Gopallawa & S. Gamage BAM 337 ( PDA) ; • ibid., BAM 203 ( PDA) ; Botiyagala, Gilimale-Erathna forest , 21 viii 1993, A. H. M. Jayasuriya & B. W. M. Wijesinghe 7478 ( PDA) ; • Gilimale, Gilimale-Erathna forest , 4 vii 1993, A. H. M. Jayasuriya & B. W. M. Wijesinghe 7415 ( PDA) ; • ibid., 27 iii 2024, H. Jayasinghe & Samarasinghe HDJ 2922 ( PDA) ; • Dotalugala forest , 27 viii 1976, S. Waas 1831 ( PDA, L 2545519 , E 01411687 ) ; • Massenna forest reserve, above Rassagala estate , 25 x 1993, A. H. M. Jayasuriya & B. W. M. Wijesinghe 7644 ( PDA) ; • Kiribathgala forest reserve , 06 iv 2024, H. Jayasinghe, D. Samarasinghe & S. Kanishka HDJ 2961 ( PDA) ; • Walankanda , 19 i 2023, H. Jayasinghe, A, Perera, I. Madawala HDJ 1947 ( PDA) ; • Delwala , 27 i 2023, H. Jayasinghe, A. Perera, I. Madawala HDJ 1956 ( PDA) • Unknown localities: s. l., s. d., s. coll., s. n., C. P. 2684 ( PDA 00002922 ; remaining specimens other than the lectotype of PDA 00002924 ; BM 000944509 , K 000859185 ).

Figures

Figure 1. Memecylon elegantulum Thwaites; A. Habit; B. Branch with an inflorescence; C. Young stem; D. Lamina upper side; E. Lamina under side; F. Dorsal view of flower; G. Inflorescence with a single flower bud; H. Inflorescence with two flowers after anthesis; J. Lateral view of flowers; K. Two inflorescences arising from a single node; L. Bracts; M. Dorsal view of flower bud; N. Dorsal view of epigynous chamber after anthesis; P. Lateral view of partially ripe fruit; Q. Dorsal view of immature fruit; R. Longitudinal section of a fruit; S. Wrinkled cotyledons.

Figure 2. Line drawing of Memecylon elegantulum Thwaites; A. Branch; B. Lamina under side; C. Lamina upper side; D. Two inflorescences arising from a single node; E. Dorsal view of the flower bud; F. Lateral view of flowers; G. Dorsal view of flower, G- inflorescence with a single flower bud, H. Bracts; J. Lateral view of partially ripe fruit; K. Dorsal view of epigynous chamber after anthesis; L. Longitudinal section of a fruit; M. Wrinkled cotyledons.

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