Homalomena amarii A.S.D.Irsyam & M.R.Hariri, 2025

Hariri, Muhammad Rifqi & Irsyam, Arifin Surya Dwipa, 2025, Jewels of the water: unveiling a new iridescent rheophytic Homalomena (Araceae) from North Sumatra, Indonesia, Phytotaxa 708 (1), pp. 99-102 : 99-101

Homalomena amarii A.S.D.Irsyam & M.R.Hariri , sp. nov. ( Fig. 1 )

Homalomena amarii is distinct from all previously described species, although it exhibits notable morphological similarity to H. hypsiantha P.C.Boyce & S.Y.Wong (2012: 148) due to its rosette forming habit, closed sheath margin, and slender peduncles. However, it differs by having obovate leaf blade (vs. elliptic), crispulate leaf margin (vs. entire), iridescent adaxially (vs. non-iridescent), solitary inflorescence (vs. up to 7 together), sessile spadix (vs. stipitate), yellowish-pink with red spots pistils (vs. greenish-white), flat to depressed stigma (vs. prominent), 2‒4 stamens per staminate floret (vs. 2), and yellowish white staminate floret (vs. white to very pale green).

Type: — INDONESIA, North Sumatra, cultivated in a private nursery from material collected in the wild [orig. coll. 20 August 2022, AH Sitompul s.n.], voucher 19 April 2025, MR Hariri 857 (holotype FIPIA!, isotype BO!).

Small rheophytic rosette-forming herbs up to 13.5 cm in height. Stem ca. 12 mm long, brown, glabrous; internodes obscured by overlapping leaf bases. Leaves 6‒10 together; petiole shorter than the blade, 2.5‒9.4 cm long (incl. sheath), canaliculate, ribbed, purplish-brown; petiolar sheath fully adnate to petiole, up to ½ petiole length, 1.0‒ 2.5 cm long, margin entire with hyaline, closed, apex truncate, purplish-brown; leaf blade obovate, 3.2‒9.7 × 1.5‒4.0 cm, base cuneate to strongly oblique, margin crispulate, apex apiculate for ca 2 mm long, adaxial leaf surface glossy green to blueish, iridescent, abaxial leaf surface pale green, fleshy; midrib impressed adaxially, raised abaxially, purplish-green to green abaxially; primary lateral veins 4‒12 on each side. Inflorescence solitary, erect; peduncles slender, up to 8.5 cm long, reddish-brown to lime green, glabrous. Spathe without constriction, ca. 15.8 × 3.7 mm, apex mucronate for ca. 2.6 mm long, exterior and interior smooth, brownish-green on both sides, inflating at anthesis and opening by a very narrow longitudinal slit, subsequently closing and enclosing the spadix. Spadix up to 12.4 mm long, sessile; pistillate floret zone ca. 2 mm long, ca. 1/5 the length of the staminate floret zone; pistils in 2‒3 whorls, dense, globose, 0.60‒0.85 mm in height, 0.75‒0.80 mm in diam., yellowish-pink with red spots; stigma sessile, flat to depressed, 0.25‒0.35 mm in diam., creamy yellow; staminode 1 each pistillate floret, globose, sessile, ca. 1/3 the height of the pistil, 0.35‒0.45 mm in height, 0.25‒0.40 mm in diam., cream; staminate floret zone ca. 11 mm long, cylindric, apex acute, yellowish-white; staminate florets densely arranged, 1.0‒2.3 × 1‒1.4 mm, consisting of 2‒4 stamens, thecae creamy white to pale ivory with apex almost transparent, globose, 0.50‒0.60 × 0.45‒0.65 mm, each opening by a broad terminal pore. Fruiting spadix, fruits, and seeds not observed.

Distribution:— The species is currently known exclusively from its type locality, with no additional populations documented to date. To prevent exploitation and ensure in situ conservation, the precise location of this species is intentionally omitted.

Habitat and Ecology:— This species inhabits rheophytic microhabitats, occurring in rock crevices within the channel of a slow-moving river at elevation ± 250 m asl.

Etymology: —The specific epithet amarii is designated in honor of Amar Husin Sitompul, the collector of the type specimen of this new species.

Note: —Based on its morphological characteristics, H. amarii is assignable to the Chamaecladon supergroup (SG). As defined by Ng et al. (2011), this informal taxonomic grouping comprises predominantly small-sized, often rheophytic species. Diagnostic features of the Chamaecladon SG include an unconstricted spathe, staminate florets bearing 2‒3 stamens, and pistillate florets accompanied by interpistillar staminodes. The overall morphology of H. amarii conforms well to this circumscription.

Figures

FIGURE 1. Homalomena amarii. A. Several individuals in the natural habitat; B. Several individuals in cultivation; C. Adaxial and abaxial leaf surfaces; D. Close-up view of petiole and apex of the sheath; E. Inflorescence; F. Spathe (18×); G‒H. Spadix (28.7×); I. Closeup view of pistils and staminodes (60.9×); J. Close-up view of staminate florets (Photos A and B were taken by A.H. Sitompul).