Homalomena ibanorum [S.Y.Wong & P.C.Boyce ]

Homalomena ibanorum

General description:

Moderately stout evergreen herbs to ca. 1.5 m tall, vegetative tissues very weakly aromatic. Stem pleionanthic, oldest portions creeping and rooting, partially subterranean, active portion erect, ca. 3 cm thick, pale green; internodes to ca. 5 mm long, obscured by overlapping petiole bases. Leaves up to 20 together, rather erect; each shoot module subtended by single prophyll, ca. 10 cm long, medium green, margin deep red, persistent; petiole 18 - 55 cm long x ca. 5 mm diam., adaxially shallowly grooved, the groove extending to the insertion of the blade, rounded abaxially, D-shaped in cross section, semi-glossy medium green; petiolar sheath open, 8 - 20 cm long, 1/3 - 1/2 length of petiole, wings long-persistent, rather membranous, pale green, the margins red; blade broadly cordate to almost deltoid, 15 - 29 cm long x 12 - 20 cm wide, coriaceous, glossy medium green adaxially, paler green and matte abaxially, with a ca. 1 - 2 mm wide red margin, apex acuminate and then mucronate for ca. 4 mm, base weakly cordate to almost truncate; midrib prominently rounded-raised abaxially, adaxially slightly impressed, up to 4 mm wide; with 6 - 8 primary lateral veins on each side, diverging at 30° (distal) to 90° (proximal) from the midrib, primary lateral veins abaxially raised, adaxially impressed; interprimary veins ca. 1/3 width of the primary lateral veins, regularly interspersed, flush with the blade adaxially, abaxially almost raised or faint; secondary venation somewhat conspicuous to weakly flush with the blade on both sides, tertiary venation invisible; all veins running into a weakly defined thickened intermarginal vein; intermarginal vein somewhat inconspicuous abaxially, adaxially almost invisible. Inflorescences up to 6 together, each subtended by a small narrowly triangular prophyll, sub-erect at anthesis, later declinate; peduncle to ca. 12 cm long x ca. 4 mm diam., medium green. Spathe stiff, somewhat fleshy, tightly furled prior to anthesis, lower spathe inflating and spathe limb gaping at pistillate anthesis, spathe limb opening wide at staminate anthesis and spadix extending and slightly protruding; spathe later closing to enclose spadix, ca. 7.5 cm long x ca. 1.75 cm wide at anthesis, exterior semi-glossy pale green, the ventral sides paler than the dorsal, and with the margins and distal-most part of the limb red-stained, interior white with red margins; lower spathe broadly ovoid, shorter than the limb, ca. 7 cm long; spathe limb narrowly ovoid with a terminal mucro 4 - 5 mm long, in all ca. 5 cm long. Spadix ca. 7 cm long x ca. 5 mm diam., stipitate; stipe ca. 1 cm long (i.e., ca. half the length of the pistillate flower zone), glossy white; pistillate zone cylindric, nearly 1/2 the length of the spadix, ca. 3.2 cm long; pistils densely arranged, globose, ca. 1.5 mm tall 3 ca. 1 mm diam., greenish white, style not differentiated; stigma convex-topped, much wider than the pistil, ca. 1 mm tall x 1.5 - 2 mm diam., mostly three-lobed, semi-translucent, glossy greenish; most pistils associated to a single interpistillar staminode, occasionally (basal-most flowers) with 2 - 3 staminodes; interpistillar staminodes with a very slender stalk and an expanded top, ca. 0.5 mm long, ivory while; suprapistillar interstice zone 1 - 2 mm long, partly naked above for ,1 mm; staminate zone narrowly conic, about half the length of the spadix, 1/4 - 1/3 held within lower spathe chamber, ca. 2.7 cm long, apex obtuse, ivory white; staminate flowers densely arranged, trapezoid to hexagonal in plan view, each flower consisting of 4 stamens, lowermost 1 - 2 rows of flowers sterile, and uppermost also sterile, each stamen over-topped by a large, flat connective. Infructescence with spathe turning green with the red margins and staining darkening. Fruits exposed by basal tearing and upward splitting of the persistent spathe; fruits oblong-ovoid, c. 5 mm long 3 3 mm wide, initially green, ripening semi-translucent dirty yellowish, fruits smelling and pulp tasting of overripe pineapple; seeds many, ellipsoid, ca. 1.5 mm long, longitudinally weakly ribbed.

General Description Reference:

WONG SIN YENG, Hoe Yin Chen, Tung Lay Soon, Peter C. Boyce, 2013. Studies on Homalomeneae (Araceae) of Borneo XIII – New Species of Homalomena

Distribution Reference:

WONG SIN YENG, Hoe Yin Chen, Tung Lay Soon, Peter C. Boyce, 2013. Studies on Homalomeneae (Araceae) of Borneo XIII – New Species of Homalomena

Ecology Reference:

WONG SIN YENG, Hoe Yin Chen, Tung Lay Soon, Peter C. Boyce, 2013. Studies on Homalomeneae (Araceae) of Borneo XIII – New Species of Homalomena

Distribution:

Homalomena ibanorum is restricted to east of the Lupar Line (see, e.g., Heads, 2003), occurring from the eastern half of Betong Division (W central Sarawak) to the northern part of Miri Division (NE Sarawak), and also into SW Brunei.

Ecology:

Lowland moist evergreen forest primarily on yellow clays, only very infrequently occurring on shales (e.g., near Kapit); below 200 m asl.

Taxonomy

Taxonomic Notes:

Homalomena ibanorum is assigned to the Borneensis Complex by the possession of open petiolar sheaths with the wing margin eventually marcescent, the leathery leaf blade with little or no posterior lobe development, and the base broadly truncate, the few primary lateral veins, and the lower spathe longer than spathe limb. The spadix most closely resembles that of H. borneesis Ridl., but is differentiated by the longer stipe (ca.1/2 vs.ca. 1/3 thelength of the pistillate flower zone), interpistillar staminodes with smooth (not papillate) clavate tops, and less well-demarcated, smaller staminate flowers (ca 1.7 mm vs ca 2.5 mm wide). In the obscure small staminate flowers H. ibanorum approaches H. clandestina P.C.Boyce, S.Y.Wong & Fasih., with which H. ibanorum also shares interpistillarstaminodeswithsmoothclavate tops, but from which it differs by a blunt-tipped (not pointed) staminate flower zone, and a much shorter spadix stipe. Homalomena ibanorum appears to be genuinely widespread, with a confirmed range of 450 km SW - NE. This is in marked contrast to other described species of the Borneensis Complex (indeed, in contrast to most other Homalomena) which are much more restricted in their distributions. One possible explanation is that H. ibanorum appears most often associated with lowland yellow clays, one of the most widespread ecologies in Sarawak whereas other species are either associated with specific geologies (shales: H. clandestina; volcanic derived clays: H. tirtae Asih, Kurniawan & P.C.Boyce), or occur on isolated mountain blocks (H. borneensis; H. ovata Engl.). A plant closely resembling H. ibanorum is known from the basalts of Bukit Quoin, Tawau, E Sabah, but has yet to be observed fertile. It is most likely a localized undescribed endemic.

Homalomena ibanorum differs from all other species of the Borneensis Complex by the combination of the leaf blades adaxially glossy green with both surfaces with a red margin, the red margins to the petiolar sheaths, prophylls and cataphylls, and spathe limb, the spathe limb exterior distally stained red spathe and spadix stipe ca. one half (vs. no more than one quarter) the length of the pistillate flower zone.

Taxonomic Notes Reference:

WONG SIN YENG, Hoe Yin Chen, Tung Lay Soon, Peter C. Boyce, 2013. Studies on Homalomeneae (Araceae) of Borneo XIII – New Species of Homalomena

CATE Araceae

Araceae

Homalomena ibanorum S.Y.Wong & P.C.Boyce

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