Homalomena brachygyna, J.Collantes, K.Z.Hein, & R.Bustam., 2024

Collantes, John Paul, Chua-Mangussad, Vernaluz, Hein, Khant Zaw & Bustamante, Rene Alfred Anton, 2024, Homalomena brachygyna (Araceae), a new species from Palawan Island, Philippines, Phytotaxa 664 (1), pp. 59-67 : 60-64

Homalomena brachygyna, J.Collantes, K.Z.Hein, & R.Bustam. , sp. nov. ( Fig. 1 & 2 )

Homalomena brachygyna differs from described Homalomena species in the Philippines by having narrowly ovate-sagittate to triangular hastate leaf blades, ovoid ellipsoid spathes without constriction and bluntly ellipsoid to subcylindric staminate zone. In overall appearance , H. brachygyna closely resembles H. passa S.Y.Wong & P.C.Boyce in Wong et al. (2013: 21) but differs by the absence of pellucid vein-like glands on the abaxial surface of the leaf blades (vs. presence), shorter spathe that is 4.2–4.4 cm in length (vs. ca. 5 cm), shorter pistillate zone (3.9–5.0 mm vs. ca. 8 mm), pistillate zone ratio 1/4 to <1/3 of spadix length (vs. 1/3), interpistillar staminodes shorter than the associated pistils (vs. slightly exceeding the associated pistils), and anthers overtopped by a large connective (vs. anthers lacking an expanded connective).

Type:— PHILIPPINES. Palawan, Municipality of San Vicente, Barangay New Agutaya , on riparian forest, ca. 250 m elevation, 20 August 2019. V.Mangussad NA#34 (holotype PNH-sheet!, CAHUP-spirit!; isotype PPC-sheet!) .

Medium-sized, clumping, evergreen, aromatic (reminiscent of Canarium ovatum L. resin), mesophytic herb up to 34.5 cm tall. Stem epigeal, erect, leafy, later older parts leafless and decumbent with active tip ascending, 2.4–2.8 cm in diameter, older portions of stem brown to light brown; roots 6–7 mm in diameter or less, tough, flexuous, white to pale brown, young part of the roots velvety. Leaves up to ca. 8 together per shoot, spirally arranged; petiole erect, older ones ascending to spreading, 17–37 cm long, pale green at the basal portion, green at the middle portion especially near the part with the sheaths then turning to pale green again near the petiole-lamina junction, with broken darker green longitudinal striae, glabrous, non-sheathing portion terete turning very shallowly canaliculate near the lamina junction, 0.55–0.65 cm in diameter above petiolar sheath; petiolar sheath 10.2–14.6 cm long, 1/3 to 1/4 of petiole length, persistent, with wings 0.7–0.8 cm proximally, tapering distally, membranous to thinly coriaceous, pale green to light green, margins slightly incurved, minutely hyaline at the edge; leaf blade narrowly ovate-sagittate to triangular hastate, 14.0– 22.2 cm long by 8.2–13.1 cm wide, slightly coriaceous, glabrous on both sides, semi-glossy and dark green adaxially, slightly paler matte green abaxially, margin entire and minutely hyaline; anterior lobe broadly triangularovate, apex acuminate and tubular mucronate with 3.0– 3.5 mm long mucro; posterior lobes subtriangular, about 1/5 the length of the anterior lobe, apexes rounded, sinus acute to obtuse; midrib rounded raised abaxially, 7–10 mm wide at the base, 4–5 mm wide at the center, then narrowing towards blade apex, adaxially impressed; primary lateral veins 7–9, the lower 4 arising simultaneously and associated with the posterior lobes, impressed adaxially, raised abaxially, curved towards apex when near margin; interprimary veins irregularly alternating with primaries, somewhat less conspicuous than primaries; secondary and tertiary venation more or less inconspicuous. Blooms usually up to 4 together, produced sequentially in a simple synflorescence, smelling of Canarium ovatum L. resin at anthesis; subtended by 2-keeled prophylls; prophyll white, 3.8–5.3 cm long by 1.05–1.15 cm wide, keel pale green; peduncle slender, terete, white at the base, gradually turning to darker green, with broken darker green longitudinal striae, glabrous, 12.0– 13.5 cm long, 0.2–0.4 cm in diameter at spathe insertion, erect to weakly arching at pistillate anthesis; spathe spreading at pistillate anthesis, ovoid-ellipsoid, not constricted, 4.2–4.4 × 1.0–1.5 × 1.3–1.6 cm deep at anthesis, tipped with a rostrate mucro 2–4 mm long, margins reflexing during anthesis, spathe exterior yellowish green above the base, becoming dark green at the apex, interior light green with scattered minute paler glands. Spadix 3/5 to 2/3 of the length of spathe, 2.21–3 cm long including the stipe; stipe terete, slightly oblique, 3.0– 5.2 mm long, 2.5–2.8 mm in diameter, smooth, glossy pale green; pistillate zone less than 1/3 to ¼ of the length of spadix, 3.9–5.9 mm long, 5.70–6.05 mm in diameter; pistils crowded; ovaries globose, 0.9–1.5 mm × 0.75–1.50 mm, greenish white to yellowish white; style 0.4–0.5 mm in length by ca. 0.75 mm, slightly narrower than ovary in diameter, greenish white; stigma capitate, 0.8–0.9 mm in diameter, narrower than ovary in diameter, translucent greenish white, papillate at pistillate anthesis; interpistillar staminodes narrowly obovoid, 0.90–1.15 mm long, 0.4–0.6 mm at widest point, 1/3 shorter than the height of the associated pistil, ivory-white; sterile interstice between pistillate zone and staminate zone absent; staminate zone contiguous within the pistillate zone, bluntly ellipsoid to subcylindric, 15.2–15.8 mm long, 7.50–8.05 mm at widest point, ivory; staminate florets irregularly rhombo-hexagonal in plan view, each comprised of usually 4 stamens (rarely 3 or 5 stamens), 0.90– 1.05 × 0.70–0.75 × 1.45–1.50 mm, stamen clenched-fist shaped, ca. 1.35 × 1.60 mm, anthers with 2–3 distinct thecae, each with a terminal crenate lobe, and overtopped by a large connective. Infructescence and seeds not observed.

Habitat and ecology:— The species was found on sandy to gravel or rock strewn streamsides, in crevices of boulders in partly shaded riparian forest. Notably, the combination of the short pistillate zone, much narrower spathe, and narrowly ovate-sagittate to triangular hastate shape of leaves may indicate a specific adaptation to its habitat. Additionally, the extensive roots suggest the species is adapted to fast-flowing water ( Boyce & Wong 2019). Especially, since floodwaters from strong monsoonal rains submerge the streamsides where the species inhabits. Among the observed plants species associated with H. brachygyna are mostly Palawan endemic species such as Alocasia culionensis Engler (1905: 135) , Begonia sp. , Begonia truncatifolia Bustamante et al. (2020: 217) , Codonoboea woodii ( Merrill 1925: 489) Weber in Middleton et al. (2013: 393), Cyrtandra elatostemoides Elmer (1913: 1781) , and Geophila repens ( Linnaeus 1759: 928) Johnston (1949: 281) .

Distribution:— The species is endemic and currently known from the municipality of San Vicente, Palawan Island, Philippines at an elevation of about 250 meters above sea level. Specimens of Homalomena sp. from review of digitized specimens collected from the nearby town of Taytay could reveal additional, but slightly distinct population (see Notes).

Etymology:— The specific epithet ‘ brachygyna ’ is from the contraction of the Greek words, βραχύς (brakhús, brakhýs), meaning ‘short’, and γυνή (gunḗ, gyne) meaning ‘female’. This is in reference to the short length of pistillate zone of the new species measuring only up to 5.9 mm as compared to 8 mm or more in the group of species represented by Homalomena selaburensis .

Phenology:— Homalomena brachygyna is known to bloom from the last week of March through the first two weeks of April, in August, and last week of October through the first two weeks of November, with the type blooming in the month of August. Pistillate anthesis is followed by staminate anthesis for 2–3 days ( Hoe et al. 2016). In H. brachygyna , the total time of anthesis is 2–3 days. The blooms (i.e. the whole synflorescence) complete a total time of anthesis in about 5 days to about a week or more. No seeds or fruiting materials were collected or observed.

Proposed conservation status:— Among the continuing threats to the species are shifting cultivation or kaingin, disturbance of forests to harvest forest products for use in boatbuilding, construction, fuelwood, and charcoal-making, as well as rain-induced landslides (CCC-GGGI 2014a, b). Similarly, the known population of the species in San Vicente has no more than 500 mature individuals and is susceptible to the abovementioned anthropogenic and environmental disturbances. Based on IUCN Red List Criteria version 15.1 ( IUCN 2023), we proposed the conservation status as Vulnerable D1+2.

Notes:— Homalomena brachygyna has features morphologically close to a group of Homalomena that includes six species [viz. H. caput-gorgonis Wong & Boyce (2014: 70) , H. curvata Engler (1912: 53) , H. galbana Baharuddin & Boyce (2010: 86) , H. niahensis Boyce (2017: 94) , H. passa , and H. selaburensis Boyce & Wong (2014: 39) ] described from Borneo and Peninsular Malaysia (sensu Ng et al. 2011, Boyce 2017). The species in this group are characterized by having ovoid to ellipsoid spathes without constriction, spathes with conspicuously glandular interior surface, ellipsoid to subcylindric staminate zone, and staminate florets each comprising 3–4 stamens (Boyce 2017). However, the much shorter pistillate zone in H. brachygyna (3.9–5.9 mm vs ≥ 8 mm in other species), the absence of pellucid vein-like glands in the abaxial surface of leaf blades (vs. presence), interpistillar staminodes shorter than the associated pistils (vs. equaling or slightly exceeding), and anthers overtopped by a large connective (vs. lacking an expanded connective) is unusual within the group. Therefore, molecular analysis is required to determine the taxonomic position of the new species within Homalomena .

Aside from Homalomena passa , H. brachygyna is morphologically closest to H. galbana , but further differs in its clumping habit (vs. solitary), shorter petiole 17–37 cm long (vs. up to 45 cm long), narrower spathe 4.2–4.4 × 1.0–1.5 × 1.3–1.6 cm (vs. ca. 5 × 3 × 2 cm), pistillate zone <¼ to <1/3 length of spadix (ca. 1/3), and pistillate zone 0.25– 0.30 as long as the staminate zone (vs. 0.5–0.6 as long). Homalomena brachygyna might also be confused with H. philippinensis but differs by the size (14.0–22.2 × 8.2–13.1 cm vs. ca. 25 × 20 cm) and shape (narrowly ovate-sagittate to triangular hastate vs. cordate) of the leaves, the unconstricted, ovoid-ellipsoid spathes (vs. slightly constricted, oblong), stipitate spadix (vs. sessile), interpistillar staminode shorter than the associated pistil (vs. equal in length) among other characters.

During review of digitized specimens of Homalomena species from Palawan, specimens (Merrill 9474) (K!, P, US!) ( RBG Kew 2021, MNHN 2023, Orrell 2023) showed morphological resemblance to Homalomena brachygyna . This taxon was collected in April 1913 by Elmer D. Merrill at Lake Manguao, in the town of Taytay in Palawan. Specifically, the specimen agrees with the description of H. brachygyna particularly in the size of the leaves 16.25– 20.10 cm × 12.6–13.2 cm (vs. 14.0– 22.2 cm × 8.2–13.1 cm in H. brachygyna ), the narrowly ovate-sagittate to triangular hastate leaf shape, the unconstricted, fornicate spathe, and pistillate zone 4.5–4.8 mm long (vs. 3.9–5.9 mm long), but differs in its spathe that is 2.5–3 cm long (vs. 4.2–4.4 cm long), spadix that is 1.5 cm long (vs. 2.21–3.00 cm long), and staminate zone 6.8–7.2 mm long (vs. 15.2–15.8 mm long). Further exploration in the area, particularly in the nearby municipality of Taytay, could eventually uncover subpopulations of this new species, indicating a slightly broader distribution than previously documented.

Figures

FIGURE 1. Homalomena brachygyna. A. Habit of whole plant, B. Leaves, adaxial view, C. Leaves, abaxial view, D. Unopened bloom, E. Adaxial view of 3 prophylls (L) and abaxial view of 3 prophylls (R). F. Stem, G. Close-up view of roots, H. Petiole, cross-section, I. Stipe, J. Leaf apex, K. Spathe, side view (L), and bloom at pistillate anthesis (R), L. Spadix (L) and its longitudinal-section (R), M. Close up view of pistillate zone during pistillate anthesis, N. Pistil, showing ovary, and stigma, O. Interpistillar staminode, P. Cross-section of ovary, Q. Close up view of staminate zone during staminate anthesis, R. Stamen, top view (L), and side view (R). Photos from holotype V.Mangussad NA#34. All photos by John Paul Collantes.

FIGURE 2. A. Habit of whole plant, B. Leaves, C. Unopened bloom, D. Prophylls, E. Spathe, side view (left), and bloom at pistillate anthesis (right), F. Spadix (left) andits longitudinal-section (right), G. Stipe, H. Cross-sectionof petiole, I. Pistil, showing ovary,and stigma, J. Interpistillar staminode, K. Cross-section of ovary, L. Stamen, top view (left), and side view (right). Illustrated from V.Mangussad#34 by Julieferd Torres.