Ridsdalea philippinensis R.Bustam. & Pelser, 2022

Ridsdalea philippinensis R.Bustam. & Pelser View in CoL , sp. nov. — Fig. 1 View Fig , 2 View Fig

A species that is unique among all currently described species of Ridsdalea in displaying a combination of flowers with a corolla tube that is distinctly inflated at its apex and anthers that do not emerge from it. — Type: PTI 4 with William Cabanillas & Lea Magarce-Camangeg (holo PNH; iso FEUH, PSU, USTH), Philippines, Palawan, El Nido-Taytay Managed Resource Protected Area (ENTMRPA), Municipality of El Nido, N11°10'44.4" E119°23'19.7", c. 150 m, 6 June 2020.

Small tree, to 3 m high. Bark of stem and branches fissured, blackish grey to light brown. Young twigs smooth, glabrous, green when fresh. Leaves usually placed in branch segments consisting of two nodes with the proximal leaf pair subtended by a relatively long internode, but the distal node bearing only one normally developed leaf (the other vestigial,acicular,c. 1–1.5 mm long) and subtended by a very short internode, resulting in a pseudo-ternate phyllotaxy. Stipules caducous, triangular to ovate, 2–3 by 1.5–3 mm, apex narrowly acute, adaxial surface with colleters at the central portion and densely pubescent, abaxial surface glabrous. Petioles 2–7 mm long, adaxially canaliculate, abaxially rounded, glabrous. Leaf laminae narrowly elliptic, 5.6–9.4 by 0.9–2.3 cm, (2.9–)3.7–6(–6.7) times longer than wide, base attenuate, apex acute or acuminate, chartaceous, abaxially pubescent when young, glabrescent; midrib on adaxial side slightly depressed, slightly raised abaxially; secondary veins 6 or 7 pairs, adaxially flat, raised below. Inflorescence terminal, but seemingly axillary following branching, compact simple cyme, glabrous; peduncle 2–3 by 1.5–2 mm. Flowers 2 or 3 per cyme; pedicels c. 1.5–2 mm long. Calyx tube (including ovary) urceolate to tubular, 9–11.6 by 2.7–3.2 mm, indumentum only visible at 10 × magnification, basal part sparsely pubescent becoming denser towards the apex; calyx lobes 5, triangular, 1–2 mm long, apex narrowly acute, margin pubescent. Corolla 7.3–8.5 cm long, white;

15

mm corolla tube 66–68 mm long, abruptly inflated at apex; basal part of tube 45–50 by c. 1.55 mm, outer surface glabrous, inner surface villous; apical part of tube 12– 20 by 9–12 mm, outer and inner surface glabrous, speckled with bright-clear red to dark red spots; corolla lobes sinistrorse, 5, ovate, 21–30 by 12.8–14.9 mm, c. 0.22 mm thick, base slightly cordate and with a few bright-clear red to dark red spots, apex obtuse to slightly acute, glabrous. Stamens 5, not emerging from the corolla tube; anthers linear with 4 parallel groves, 12–13 by c. 1.75 mm. Style and stigma not emerging from the corolla tube, 63–66 mm long; style terete, 54–58 by c. 1 mm, smooth, glabrous; stigma clavate, 8–9 mm long. Immature fruits obovoid and crowned with a persistent calyx, c. 24 by 17 mm, locules 2, placentation axile; mature seeds not observed.

Distribution — Ridsdalea philippinensis is endemic to El Nido, Palawan ( Philippines).

Habitat & Ecology — Tower karst formation.Altitude:c. 150 m. Flowering: June.

Conservation status — The first author has continually explored the El Nido-Taytay Managed Resource Protected Area since 2014, but the new species has thus far only been docu- mented on one tower karst formation of approximately 250 hec- tares situated directly beside highly urbanized areas, where it grows on the exposed limestone tower karst summit and the upper sides of the sheer cliff face. Due to the inaccessibility of most of the other tower karst formations in El Nido, these areas have not yet been fully explored. It is therefore possible that R. philippinensis also exists at other sites. We thus propose this species to be Data Deficient ( IUCN 2001).

Notes — Ridsdalea philippinensis is unique among Male- sian Ridsdalea species in having a corolla with a distinctly inflated apex. However, it is perhaps most similar to R. merrillii (Elmer) J.T.Pereira from Borneo ( Fig. 1 View Fig ) and the Philippines and R. puffiana J.T.Pereira from Borneo.Amongst others, these three species have leaves that always show at least some pubescence when young, stipules that are shorter than 10 mm, a calyx that is glabrous or at most with pubescence that is only visible at 10 × magnification, and that have relatively few flowers per cyme ( Pereira 2008, 2016). However, the corolla throat of R. philippinensis is speckled and glabrous inside, whereas both R. merrillii and R. puffiana have a pubescent corolla throat that is not speckled ( Pereira 2016). In addition, the leaves of R. philippinensis are typically narrower (0.9–2.3 cm wide) than those of R. merrillii ((1.5–)4–8(–10) cm; Pereira 2008). Further, R. philippinensis has a much shorter corolla tube (66–68 mm) than R. puffiana ((80–) 105–145 mm), as well as longer anthers (12–13 mm vs 6–12 mm) ( Pereira 2016).

Ridsdalea philippinensis View in CoL also bears some resemblance to R. sootepensis View in CoL and R. thailandica View in CoL from Thailand and Laos. For example, all three species have a corolla tube that is inflated near the apex and a speckled corolla throat ( Craib 1911, Tirvengadum 1983). However, the anthers of R. sootepensis View in CoL and R. thailandica View in CoL clearly extend beyond the corolla tube ( Tirvengadum 1983), whereas those of R. philippinensis View in CoL are contained within its apical portion. Both species also have smaller flowers than R. philippinensis View in CoL (e.g., corolla tube less than 55 vs 66–68 mm long; corolla lobes up to 20 vs 21–30 mm long) ( Craib 1911, Tirvengadum 1983). In addition, the calyx of R. sootepensis View in CoL is distinctly pubescent (vs with indumentum that is only visible at 10 × magnification) and has longer calyx lobes (i.e., 2.3–4.2 vs 1–2 mm long) ( Craib 1911). Further- more, the leaves of R. sootepensis View in CoL are generally narrower than those of R. philippinensis View in CoL (length/width ratio 2.6–4 vs (2.9–)3.7–6(–6.7)). Ridsdalea thailandica View in CoL most conspicuously differs from R. philippinensis View in CoL in having corolla lobes that are of about the same length (vs less than half as long) as the corolla tube ( Tirvengadum 1983). The apex of its corolla tube is also much less distinctly inflated and c. 5 mm instead of 9–12 mm wide at the throat ( Tirvengadum 1983).