Argostemma mirae Blasco, Tandang & Alejandro

Blasco, Freddie A., Tandang, Danilo N. & Alejandro, Grecebio Jonathan D., 2024, Argostemma mirae (Rubiaceae) a new species from Tago, Surigao del Sur, Mindanao Island, Philippines, Phytotaxa 640 (1), pp. 65-70 : 66-69

Argostemma mirae Blasco, Tandang & Alejandro , sp. nov. ( Fig. 1 ).

Type— PHILIPPINES. Mindanao Island , Surigao del Sur, Tago, Badong , Mt. Tingtingan , elev. ca. 10m. It grows on a shady mossy limestone forest on a lower elevation. 22 May 2022 Freddie A. Blasco 22-002 (holotype PNH, isotype USTH)

Diagnosis — Argostemma mirae closely resembles A. solaniflorum Elmer over A. arachnosum Merrill and A. distichum Valeton in having erect, branching and pubescent stems, glabrous stipules, pubescent petioles, oblanceolate leaves, dark green lamina, abaxially pubescent leaf surface, acute base, margin entire, pubescent calyx lobes, corolla lobes surface abaxially pubescent, white corollas and pubescent pedicel but differs in having shorter stems 10–13 cm. (vs. 16), stipules broadly ovate (vs. oblong), smaller leaf blades 2.5–3. × 1– 1.3 cm (vs. 7 × 2), acuminate apex (vs. obtuse), adaxially glabrous leaf surface (vs. pubescent), lateral leaf veins 4–5 pairs (vs. 7–8), inflorescences 2 (vs. 5), 4 calyx lobes (vs. 5), 4 corolla lobes (vs. 5 star-shaped), corolla lobes surface adaxially glabrous (vs. pubescent), longer pedicel 15–17 mm (vs. short 8), anthers length 3–4 mm (vs. 7) and opening by longitudinal slits (vs. apical pore).

Lithophytic herb, Stem, 10–13 cm tall, 2.5–3 mm in diameter, pubescent, erect and branching, internodes 5–7 mm long, terete. Stipules persistent, broadly ovate, 5–6 × 3–4 mm, glabrous, apex acuminate, margin entire. Leaves glabrous, glossy, oblanceolate, petiole 4–5 mm long, terete, pubescent, blade 2.5–3. × 1–1.3 cm, apex acuminate, margin entire, obliquely acute base, adaxial surface glossy, glabrous, dark green with prominent midrib and veins, abaxial surface light green and hairy with distinct pubescent midrib, lateral veins 4–5 pairs. Inflorescence terminal to axillary, cymose, 2–flowered, peduncle pilose, 8–10 mm, bracts 3–4 × 1–2 mm persistent and pubescent, ovate, pedicel 15–17 mm long. Calyx lobes 4, triangular to narrowly triangular, gamosepalous, hypanthium, infundibuliform, pubescent. Corolla lobes 4, white, adaxially glabrous, abaxially pubescent 6–7 × 3–5 mm, broadly ovate when young, narrowly triangular when mature, apex acuminate. Stamens 4, 5–6 mm long, filaments short, anthers yellow, 3–4 mm long. Ovary inferior, bilocular, ovules numerous, style 4–5 mm long, stigma 2–3 mm long, simple, exserted. Fruit obovoid, 5–6 × 4–5 mm, pubescent, crowned by a persistent calyx, opening by longitudinal slits.

Phenology —Observed flowering and fruiting in April to May when the dry season is at its peak.

Etymology —The species is named after Mrs. Evangeline A. Mira to honor her 45 years of service to Saint Theresa College of Tandag. Ma’am Mira, as she is fondly called by her students, colleagues and friends is a biology and language teacher and a dear friend.

Distribution and Ecology —Endemic to the province of Surigao del Sur, CARAGA Region Eastern Mindanao, Philippines. It grows on a shady, mossy limestone forest on a lower elevation in Mt. Tingtingan, Badong, Tago, Surigao del Sur, elev. 10 m asl.

Notes— Argostemma mirae superficially resembles A. distichum Valeton in having branching stems, broadly ovate stipules, dark green lamina, entire margin, 4 glabrous white corollas, and longitudinal slits dehiscence. However, the new species is distinct in having erect and longer stems (vs. creeping), larger leaves, acuminate apex (vs. sharplyacute), numerous major leaf veins 4–5 (vs. 1–2), longer pedicel and anthers, and 2-flowered inflorescence (vs. multi-flowered 5–6). It is also comparable to A. arachnosum Merrill in having pubescent stems, glabrous stipules, acuminate apex, pubescent calyx lobes, white corollas, and longitudinal slits dehiscence, but differs in having shorter erect stems (vs. creeping, solitary), dark green lamina (vs. light green with green sparse), acute leaf base (vs. cordate-rounded) longer pedicel 15–17 mm (vs. 10–12 mm.), 2-flowered inflorescence (vs. multi-flowered 10–25), and 4 corolla lobes (vs. 5 star-shaped). Table 1 offers a thorough comparison of A. mirae and its allied species.

Proposed IUCN category:— Mt. Tingtingan has not been explored by any researchers due to the peace and order situation, which can make it hard to assess the conservation status of the species. The location is not a protected area. Although there is only one population currently known, there are several individuals found in a moist shady, mossy limestone in an undisturbed forest. We recommend a conservation status of data deficient [DD] ( IUCN, 2022).

Figures

FIGURE 1. Argostemma mirae Blasco, Tandang & Alejandro. A. Habit & Habitat; B. Young flower; C. Matured flower; D. Fruit.