Rose taro (Alocasia roseus) from Aceh, Indonesia, similar to Alocasia flemingiana and Alocasia arifolia

NEWS - Rose taro (Alocasia roseus Asih & Yuzammi, sp. nov.) from Aceh Besar District, Sumatra (Indonesia) was found to produce a striking inflorescence and is morphologically similar to Alocasia flemingiana Yuzammi & A.Hay and Alocasia arifolia Hallier f.

Alocasia (Schott) G.Don (Araceae Juss.) consists of 100 species, but recent studies suggest there may be 41 additional undescribed species. The genus is distributed in tropical and subtropical Asia from Malesia to Oceania and mainland Australia.

Borneo is considered to have the richest Alocasia diversity and endemism. However, the diversity and distribution of Alocasia is poorly understood in the Indonesian archipelago with about 27 known species. Prior to this study, there were 7 species recognized in Sumatra. Knowledge of Alocasia in Sumatra is inadequate.

The last taxonomic revision was conducted over 25 years ago which recognized 6 taxa of Sumatran Alocasia: Alocasia alba Schott, Alocasia arifolia, Alocasia inornata Hallier f., Alocasia longiloba Miq., Alocasia kerinciensis A.Hay, and Alocasia puber (Hassk.) Schott. Alocasia macrorrhizos (L.) G.Don is listed as an introduced species to Sumatra.

Alocasia is known as one of the most popular ornamental plants, sought after and traded by hobbyists and the general public, many species are collected directly from the forest and traded illegally.

A. roseus is only known from Aceh Besar, Sumatra Island. It grows on forest slopes, in shady and humid places. The specific epithet, roseus, is based on the pale pink staminode appendages. This appendage color is rare in this genus.

The new species is only known from a single location in the forest near Kueh Kemukiman Keude Bieng, Kueh Village, Aceh Besar District, Aceh Province, Indonesia. Because further populations may occur, the researchers chose to assess the status as Data Deficient (DD) according to the IUCN Red List criteria (2022).

The species is included in the informal group “Macrorrhizos” (sensu Hay 1998) because of the paired inflorescences, the spathe constriction parallel to the sterile cleft of the spadix and the synconent covering of the thecae. It is the second species, besides A. balgooyi, in the Macrorrhizos group that lacks a naked sinus in the posterior lobe.

A. roseus also has a different appendix color from other species in the Macrorrhizos group. The pink appendix color is a rare color and is only found in A. melo and A. princeps.

New species similar to A. flemingiana and A. arifolia, but with greyish-green adaxides and pale red to greenish-purple or pale brownish-green abaxial leaves, no veins, no glabrous sinuses and pale pink appendages (vs. medium to dark green adaxides and yellowish/paler green abaxial leaves, inconspicuous to conspicuous veins, glabrous sinuses up to 3 cm long and pale cream/apricot appendages).

DESCRIPTION

Rose taro (Alocasia roseus) is a species of plant in the Araceae (Aroideae, Colocasieae), small herb c. 55cm tall; rhizome erect; leaves several together; petiole 34–38 cm long, pale dull green, glabrous, faintly mottled greenish, sheathing in the lower about 1/3 of its length, pale dull green.

Blades leathery, sagittate, grayish green adaxially, reddish to greenish purple to pale brown greenish abaxially, margin entire; anterior lobe 12.8–14.4 cm long, 9.7–11.6 cm wide, the widest is base of anterior lobe, tip acuminate, 7 mm long.

Anterior costa with 4–5 primary lateral veins on each side, proximal ones diverging at 76–96° on each side then running to submarginal vein, distal primary veins diverging at 40–45° on each side, primary vein prominent adaxially then forward to marginal becoming flush to lamina, prominent abaxially, with inconspicuous axillary glands, secondary and tertiary venation flush to lamina adaxially, rather prominent and conspicuous abaxially then running to conspicuous submarginal vein inserted c. 1.5 mm from margin, interprimary collective veins absent.

Posterior ribs diverging at 60–80°, not naked in the sinus; posterior lobes acute, 6–7.2 cm long.

Inflorescences solitary or in pairs, subtended by green cataphylls and then dried at flower anthesis; peduncle to c. 14.6 cm long, resembling petioles in color and faintly mottled; spathe c. 9.7cm long; lower spathe ovoid, yellowish green, c. 2.3 cm long, c. 1.8 cm diam,

Limb lanceolate, yellow to greenish, erect then tilted 45° after 3 days, separated from the lower spathe by a constriction at the base of male flowers or at top sterile interstice (to the midpoint of the male zone); spadix shorter than the spathe, c. 7 cm long, shortly stipitate, 2–4 mm, whitish-green, cylindric.

Female zone cylindrical, 0.9–1 cm long, 0.9 cm wide; ovaries subglobose, green, stigma raised on a style 0.5–1 mm, conspicuously, (2–)3–4-lobed, pale yellow; sterile interstice cream-coloured, not attenuate, 0.4–0.5 cm long, narrower than male zone, with 4–5 whorls of rhomboid synandrodia;

Male zone cylindrical, cream-coloured, 1.1–1.2 cm long; synandria rhombohexagonal to somewhat irregular, with the synconnective overtopped the thecae; thecae opening by apical pores; appendix pale pink, gradually tapering to a blunt point, faintly irregularly channeled, c. 3.5–4.2 cm long, slightly wider than the male zone; fruit unknown.

Original research

Asih NPS, Erlinawati I, Yuzammi, Hadiah JT (2024). The Araceae of Sumatra I: A new species of Alocasia from Aceh, Indonesia. PhytoKeys 249: 223-229, DOI:10.3897/phytokeys.249.133737

Dlium theDlium