Acranthera philippinensis Merr. (1913:32)

Ordas, Jorge Anton D., Zamudio, Sarah Grace S. & Docot, Rudolph Valentino A., 2023, A rare Philippine plant found again after almost a century: the rediscovery and lectotypification of Acranthera philippinensis (Rubiaceae), Phytotaxa 578 (1), pp. 136-140 : 137-139

Acranthera philippinensis Merr. (1913:32) , Figure 1

Type: — PHILIPPINES. ZAMBOANGA, Sax River , 27 November 1911, E . D. Merrill 8309 (lectotype L0058764 !, designated here; isolectotypes: US 00137842!, P03801517 !) .

Description: —Unbranched pubescent ground herb, 40–70 cm tall, with tissues that turn brown to black when dry. Stem angular, densely pilose with brown to graying trichomes. Leaves opposite; petioles 1.4–7.0 cm long, strigose to strigulose, often with lenticels; leaf-blades thinly chartaceous to membranous, ovate to oblong-lanceolate, 8.5–25.0 × 3.3–10.0 cm, adaxially sparsely tomentose to villous, densely tomentose along the midrib and lateral veins, abaxially sparsely puberulent, densely tomentose along the midrib and lateral veins, base cuneate or obtuse, apex acute to slightly acuminate, margins ciliolate; lateral nerves 7–10 on each side, reticulated, slightly depressed adaxially, prominent abaxially; stipules persistent, broadly ovate to triangular, with a prominent but decurrent keel, 16–25 × 5–7 mm, densely villose, apex acute, margins ciliolate. Inflorescences of one or two terminal cymes comprising 15–20 flowers, 2.0– 3.5 cm in diameter, primary and secondary peduncles 9–11 mm long, strigose to strigulose; bracts in two whorls pinkish to light red, elliptic, apex acute, pubescent, outer bracts 15–25 × 5–10 mm, sometimes with a small protrusion less than 1 mm at the base, inner bracts 11–18 × 3–10 mm; bracteoles linear, 2 mm long, pubescent; pedicel dark red, 3–5 mm long, pubescent. Flowers 4 to 6-merous; calyx ovary portion densely strigose, cylindrical, dark red, 9–11 mm long; calyx lobes 4 to 6, puberulent, elliptic to oblong, pinkish 8–10 × 3–4 mm, margins ciliolate; corolla white, hypocrateriform, 9–11 × 2–3 mm, densely pubescent outside, inside glabrous; tube 6–8 × 2–3 mm, densely pubescent; lobes broadly ovate to acute, 3.0–3.3 × 2.0–3.0 mm, apex acute to obtuse, tip hispid. Stamens 4 to 6, inserted at the base of the corolla tube, filaments 0.5 mm; anthers linear, 6 mm long, appearing connate surrounding the pistil; pistil 6 mm long, style 5 mm long, stigma globose, 1 mm long. Fruit berry-like, pink to dark red, narrowly oblong, villous to pubescent, 20 × 3–4 mm, crowned with persistent calyx lobes.

Distribution and Habitat: — Acranthera philippinensis is endemic to Mindanao, Philippines, to the provinces of Zamboanga City and Zamboanga del Sur ( Figure 2 ). It occurs along small streams or in humid forested areas in wet humus soils, at elevations of 700– 900 m. a.s.l.

In 1919, a set collection of A. philippinensis (M. Ramos & G.E. Edaño 36647) was collected in Mount Tubuan, District of Zamboanga. According to Google Maps, however, Mount Tubuan is a low-elevation mountain located in the province of Maguindanao which is outside the political borders of the District of Zamboanga in the early 1900s. Hence, we have concluded that Mount Tubuan is already an extinct name of a mountain located somewhere in the Zamboanga region and therefore, the exact location of (M. Ramos & G.E. Edaño 36647) is at this point, impossible to be determined.

Phenology: — Acranthera philippinensis flowers in October–November. Fruits are expected to be observed in January–February.

Provisional Conservation Status: —Based on the IUCN red list categories and criteria ( IUCN Standards and Petitions Subcommittee 2022), Acranthera philippinensis is categorized as Endangered (EN B2ab(iii), D): B2: area of occupancy (AOO) is estimated to be less than 500 km 2 (AOO is c. 32 km 2), a: known from two locations. Within Mount Timolan, Zamboanga del Sur, seven mature individuals were observed. Unfortunately, there are no other collections aside from the type material found along Sas River, Zamboanga City (type locality) and neighboring localities among the herbaria visited. One of the threats identified would be the continuous conversion of forests into agricultural land within the two localities’ vicinities, which would likely contribute to the decline of A. philippinensis . The assessment will be updated when more localities with habitats suitable for A. philippinensis have been explored, including those in neighboring provinces.

Notes: — Merrill (1913) described this species based on several sheets and marked it as a new generic record in the Philippines. As the sole representative of the genus in the country, it is easily recognizable from other genera by its unique floral features, and it is distinct from other Acranthera found in other countries by its numerously flowered cymes and pinkish, accrescent calyx lobes. Merrill also noted that A. philippinensis has cymes that are 7–10 cm in diameter with numerous 4 to 5-merous flowers. Our material showed that one cyme is only 2.0– 3.5 cm in diameter, and thus may have measured several cymes altogether. Our material also showed that some flowers are 6-merous as well.

Merrill indicated E. D. Merrill 8309 as the type series represented by several sheets in his 1913 protologue. As part of the Bureau of Science collection, a sheet would have been deposited in PNH. It was confirmed, however, that this was destroyed during World War II. Hence, a lectotype must be chosen from the surviving duplicates following ICN Article 9.3 ( Turland et al. 2018). Since the sheet at L has the best-preserved vegetative and reproductive parts, this study designated it as the lectotype and the remaining sheets will be considered as isolectotypes.

Additional specimens examined: — PHILIPPINES. ZAMBOANGA CITY : Sax River , 16 February 1905, R. S . Williams 2357 ( US): DISTRICT OF ZAMBOANGA: Mount Tubuan , October 1919; fl; M . Ramos & G. E . Edaño 36647 ( L, US, P); ZAMBOANGA DEL SUR: TIgbaO, Barangay LImas, MOUnt TImOlan, 7°48′00.1″N, 123°14′45.0″E, 827 m, 30 NOvember 2018, fl, R. V. A . Docot et al. ZMT18-025 ( FEUH incl. spirit, USTH) .

Figures

FIGURE 1. Acranthera philippinensis Merr. A. flowering branch, B. leaf blade, C. terminal cymes with only calyx remnants, D. cymes with flowers, and E. corolla. Photographs by R.V.A. Docot.

FIGURE 2. Geographic distribution of Acranthera philippinensis in the Philippines.