Psychotria pendens M. Bautista & R. Bustam.

Bautista, Mary Ann C., Chua-Mangussad, Vernaluz, Cervancia, Jehson & Bustamante, Rene Alfred Anton, 2024, Psychotria pendens (Rubiaceae, Psychotrieae), a new ultramafic species from Central Palawan, Philippines, Phytotaxa 649 (3), pp. 252-260 : 253-258

Psychotria pendens M. Bautista & R. Bustam. , sp. nov. ( Figures 1–2 )

Type:— PHILIPPINES, Palawan, Malinao, Mount Victoria , ca. 500 m, January 2022, MVIC26 , (holotype: PNH; isotypes: PPC, USTH) .

Description:— Psychotria pendens closely resembles Psychotria rubiginosa Elmer (1906: 25) ex Merr. (1906: 135) by having monochotomous inflorescence and oblanceolate to oblong-elliptic leaves, but differs in the large, leaf-like, valvate stipules with attenuate to acuminate cleft lobes (vs. small, valvate stipules with aristate cleft lobes), slightly corrugated leaves with the glabrous abaxial surface (vs. flat leaves with pubescent to puberulous abaxial surface), pendent inflorescence (vs. erect inflorescence), narrowly triangular bracts (vs. ovate triangular bracts), glabrous calyx (vs. pubescent calyx) ( Table 1 ).

Evergreen shrub or small tree, 1–4 m high; young stem puberulous, mature parts glabrous. Stipules valvate, semi-persistent, conspicuous, almost leaf-like, broadly lanceolate to elliptic, 2–3 cm long, apex distinctly cleft (bilobed), cleft lobes margin densely pubescent, attenuate to acuminate tip. Leaves simple, opposite; petioles 1–2 cm long, glabrescent or puberulous to pubescent; leaf blades oblanceolate to oblong-elliptic, 12–25 cm long, 4.5 – 7 cm wide, acuminate at apex, attenuate to acute at base, subcoriaceous, slightly corrugated (raised beneath, impressed above); adaxial side dark green, abaxial side light green; midrib slightly raised adaxially and prominent abaxially, secondary veins 12–16 on each side, distinctly united submarginally, tertiary venation manifest, glabrous. Inflorescence monochotomous, pendent, 10–18 cm long, pubescent to densely pubescent, indumentum drying reddish-brown; principal axis/peduncle 5–8 cm long with 4–5 primary nodes, verticillate branching at each node, branches terminating in cymules; bracts narrowly triangular, 3–4 mm long, pubescent; bracteoles ovate-triangular, ca. 1.5 mm long, pubescent. Flowers 5- merous; pedicels 1.5–2 mm long; calyx including hypanthium 2.5–3 mm, external surface glabrous, calyx lobes orbicular to broadly ovate; corolla white, corolla tube 3.5–4 mm long, glabrous, villous at throat within, corolla lobes ca. 2–2.5 mm; stamens ca. 3.5–4mm long, filaments ca. 2–2.5 mm, anthers ca. 1.5 mm, style ca. 3 mm; ovary ca. 2 mm. Fruits globoid or ellipsoid, 5–7 mm, ribbed or ridged upon drying, orange upon maturity, glabrous; pedicels 1–2 mm long; calyx limb and lobes persistent; pyrenes 2, elliptic-obovate, ribbed/ridged, endosperm ruminate.

Phenology:— The species was observed flowering during the months of January, February, and July, fruiting during the month of July.

Habitat and Ecology:— It grows with other Psychotria species in the moist and shady areas of lowland to midelevation forest (400–600 m) in Mt. Victoria.

Distribution:— Psychotria pendens is currently known from the type locality in Mt. Victoria, Palawan, Philippines ( Figure 3 ).

Etymology:— The specific epithet ‘ pendens ’ was derived from Latin, meaning ‘to hang’ in reference to the long, pendent inflorescence.

Proposed IUCN status:— Following the IUCN Red List categories and criteria ver. 16 (2024), we herein propose this species to be classified as Critically Endangered CR B1ab(iii)+2ab(iii) as the extent of occurrence (EOO) is approximately less than 100 km 2 and the area of occupancy (AOO) is less than 10 km 2. P. pendens has a restricted distribution and a relatively small number of mature individuals (less than 10 mature individuals observed in the type locality).

Notes:— The new species is quite distinct by having large semi-persistent stipules and pendent inflorescence. These characters are in contrast with other known species of Psychotria in the Philippines as most species have caducous stipules and erect inflorescence.

Molecular analysis:—To check the possible phylogenetic placement of Psychotria pendens within Psychotrieae , we sequenced the highly divergent DNA regions (rbc L, rps 16, trn L-F, nrITS). The resulting tree does not provide robust taxonomic support due to limited taxonomic sampling but based on molecular analysis, it can be inferred that the new species Psychotria pendens and the widespread Philippine species Psychotria luzoniensis (Cham. & Schltdl.) Fern —Vill. (1880: 112) are closely related to Hawaiian Psychotria and they belong to the same clade as Amaracarpus Blume (1826: 954) , Calycosia A.Gray (1860: 47) , and other Pacific (New Guinea, Fiji) species of Psychotria ( Figure 4 ). Piesschaert's (2001) pyrene data is consistent with this topology, as most species he investigated in Indonesia, the Philippines, New Guinea, and Fiji have distinct marginal pre-germination slits (PGSs) and an abaxial surface with few or incomplete ridges. These characters suggest inclusion in the Pacific clade ( Andersson 2002). The topology is also parallel to the Pacific clade presented in the broader molecular analysis of Razafimandimbison et al. (2014), which formally transferred all allied genera (including Amaracarpus and Calycosia ) to Psychotria .

Psychotria pendens and P. luzoniensis have higher affinities to the Hawaiian species, P. mariniana (Cham. & Schltdl.) Fosberg (1962: 43) , compared to other species included in the analysis. Andersson (2002) emphasized that several species from the Philippines, Borneo, Fiji, Solomon Islands, and New Guinea could be related to Hawaiian Psychotria due to their similar carpological features presented in Piesschaert's (2001) dissertation report. They all possessed long marginal PGSs with ventrally ruminate endosperm. However, the current taxonomic samples and amount of sequence data do not provide sufficient information to define taxonomic relationships. The sister-group relationship between Philippine Psychotria and Hawaiian Psychotria remains unclear. Additional sequences from Southeast Asia and the Pacific region might give a better representation of the specific relationships among the Pacific clade, including the Hawaiian and Philippine species.

On the other clade, only Psychotria manillensis Bartl. ex DC. (1830: 522) and P. cephalophora Merr. (1908: 438) have grouped with the Tropical Afro-Asian Psychotria clade. Morphologically, these two closely resemble the type species P. asiatica Linnaeus (1759: 929) . Like P. asiatica , these species exhibit the ‘classic’ Psychotria characters such as caducous stipules, ethanol-soluble seed coat pigment, and reddish-brown leaf color upon drying.

Figures

FIGURE 1. Psychotria pendens M. Bautista & R. Bustamante.A. Habit; B.Adaxial leaf surface; C.Abaxial leaf surface; D. Inflorescence; E. Flower (side view); F. Fruit (side view); G. Fruit (cross-section) H. Stipule. Illustrated by Julieferd C. Torres.

FIGURE 2. Psychotria pendens M. Bautista & R. Bustamante.A. Habit; B.Adaxial leaf surface; C.Abaxial leaf surface; D. Inflorescence; E. Flower (side view); F. Fruit (side view); G. Fruit (cross-section) H. Stipule. Photographs were taken by R. Bustamante (A), A. Langbao (B–C), M. Bautista (D–F, H), and D. Salas (G).

FIGURE 3. Type locality of Psychotria pendens in Mt. Victoria, Palawan. Dot map prepared by J.L. Bibar.

FIGURE 4. Maximum-likelihood tree showing the phylogenetic placement of Psychotria pendens within Rubiaceae. Numbers on each node represent the bootstrap support values.