Aridarum pendek

General description: 

Diminutive mat-forming obligate rheophytes to 2 cm tall. Stem creeping and rooting, 1–4 cm long, ca. 2 mm in diam., more or less obscured by overlapping leaf bases and ligule remains. Leaves few together; petiole ca. 3 mm, ca. 0.4 mm diam., adaxially canaliculate, sheathing at the extreme base, whitish green; petiolar sheath with wings extended into a very narrowly triangular ligular portion ca. 1 cm long drying dark red-brown, soon shed; blade thinly coriaceous, oblanceolate, adaxially dark green and minutely pitted, abaxially much paler with numerous minute darker glandular raised punctuations, 2.5–3 cm long 3 ca. 1 cm wide, base narrow cuneate, apex obtuse with a very short mucro ca. 0.4 mm long, margin hyaline-crispulate; midrib abaxially and adaxially slightly prominent; primary lateral veins one on each side, arise from the base of the leaf blade and running half way between the midrib and the margin from the base to the tip; interprimary venation obscure, approximately following the line of the primary lateral veins; secondary venation adaxially and abaxially very faint to completely obscure; tertiary venation forming a faint tessellate reticulum. Inflorescence solitary; peduncle relatively stout, exceeding the petioles, ca. 5 mm long x 0.4 mm diam., terete, pale green; spathe more or less ovoid, not constricted, ca. 1.5 cm long, apically beaked for ca. 0.7 mm; lower part funnel-shaped, green, persistent; spathe limb gaping at pistillate anthesis, caducous before the end of staminate anthesis, glistening white, apical
beak medium green. Spadix subcylindric to bluntly spindle-shaped, ca. 4.5 mm long, ca. 2 mm diam.; pistillate flower zone ca. 2 mm long, comprised for ca. 3 whorls of pistils, ca. 2 mm diam.; pistils crowded, sub cylindrical, ca. 0.5 mm diam., medium green; stigma sessile, discoid, about the same width as the ovary, green; interpistillar staminodes and sterile interstice absent; staminate flower zone ca. 4 mm long, comprised of 2 rows of fertile flowers; staminate flowers narrowly ellipsoid-rectangular from above, ca. 0.5 mm across, the connective not excavated, pale yellow, minutely glandular; thecae situated on the proximal and distal (with respect to the spadix axis) sides of the anther, each with a short, robust, slightly to strongly in-curved horn 0.2 mm long; appendix absent. Fruiting spathe funnel-form with a very ragged margin where the spathe limb has fallen; fruits and seeds not see not seen.

Diagnostic description: 

Aridarum pendek is unique in the genus by the combination of stout thecae horns with their bases occupying the whole upper part of the anther, and diminutive habit with the leaves closely appressed to the substrate. Similar thecae horns are found in Aridarum incavatum, from which A. pendek differs by the very much smaller habit (plants ca. 2 cm tall vs. 10–20 cm tall), the appressed (not erect) leaves with the blades ca. 3 cm (vs. 9–17 cm long), the much smaller spathe (ca. 1.5 cm long vs. 2.5–4 cm long), and spadix (4.5 mm vs. 1–1.5 cm long.)

Distribution: 

Aridarum pendek is known only from the Type locality where it seems to be very rare.

Ecology: 

Aridarum pendek occurs as a rheophyte strongly rooted to shale riverside boulders under lowland moist forest at ca. 20 m asl.

Taxonomy
Taxonomic Notes: 

An extraordinary Aridarum that, based on the morphology of the staminate flowers, appears to be allied to A. incavatum H. Okada & Mori, a vegetatively very different species from the basalts of Gunung Niut in NW Kalimantan Barat. Molecular analyses is wanting.

Taxonomic name: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith