Arthraxon

Arthraxon is a genus of herbaceous plants in the Poaceae family. It is native to tropical Africa, Madagascar, Mauritius, the Indomalaya region to Japan.

Description

They are annual plants; stems decumbent, reaching a size of 45–100 cm tall, usually rooting at the basal nodes; glabrous internodes; hairy knots; hermaphrodite plants. Pods slightly inflated, glabrous, with the margin sparse to densely hairy, the trichomes bulbous at the base; ligule 0.4–3.5 mm long, margin truncate, ciliate; blades ovate-oblong to linear-lanceolate, 0.8–7.4 cm long and 2–8 mm wide, flattened, the base slightly cordate and amplexicaule, the margins of the sub-basal area with bulbous trichomes. Inflorescence 0.4–11.8 cm long and 0.2–6 cm broad, racemes 1–30, with 1–several spikelets, rachis articulated; spikelets paired or the pedicelate spikelet reduced to a small pedicel, the 2 spikelets and one rachis internode drooping as a unit; sessile bisexual spikelets, 1.9–7.9 mm long and 0.4–1.5 mm broad, laterally compressed, with 2 florets, callus truncate, glumes equal or subequal, lanceolate, lower glume rounded, 1.7–7.7 mm long, chartaceous, with spikes on veins, upper glume 2.5–7.5 mm long, sides hyaline, chartaceous keel with spicules of different sizes, lower floret sterile, lower lemma 1.1–5.8 mm long, hyaline, glabrous, awnless, sometimes absent, lower palea absent, upper floret bisexual, upper lemma 0.5–5.8 mm long, hyaline, glabrous, awn 3–5 mm long, palea generally absent, hyaline when present, lodicules 2, 0.2–0.6 mm long, stamens 2 or 3, styles 2; pedicelate spikelets sterile, reduced to a very small, glabrous pedicel; free pedicels. Fruit a caryopsis; dotted thread.

Taxonomy

The genus was described by Ambroise Marie François Joseph Palisot de Beauvois and published in Essai d'une Nouvelle Agrostographie 111, pl. 11, f. 6. 1812. The type species is: Arthraxon ciliaris P. Beauv.

Etymology

The name of the genus derives from the Greek arthron (joint) and axon (axis), alluding to the articulated rachis.

Cytology

The basic chromosome number of the genus is x = 9 and 10, with somatic chromosome numbers of 2n = 18, 20, 36 and 40, since there are diploid species and a polyploid series.

Species

• Arthraxon ciliaris P. Beauv.
• Arthraxon lancifolius (Trin.) Hochst.
• Arthraxon linifolius Henr.