Iresine rhizomatosa Standl.

Iresine rhizomatosa plant

Family - Amaranthaceae

Stems - To +1m tall, erect or ascending, multiple from the base, glabrous, swollen at the nodes, green-striate, carinate below, branching, fistulose, herbaceous.

Iresine rhizomatosa stem

Leaves - Opposite, petiolate. Petioles to 5cm long, winged by decurrent leaf tissue, reddish at the base, glabrous. Blades ovate to ovate-lanceolate, entire, deep green above, light green below, glabrous or with a few hairs on the veins below, acute, to 15cm long, +/-8cm broad.

Iresine rhizomatosa leaves

Inflorescence - Pistillate flowers in axillary and terminal panicles to +15cm long. Lower-most branches of the panicles subtended by small bracts. Flowers sessile, only slightly overlapping, the rachillae clearly visible between the individual flowers. Each flower subtended by a large tuft of pillose hairs. The hairs persistent in fruit and acting as a transport mechanism. Branches of the pistillate inflorescence typically ascending or erect. Staminate inflorescences paniculate, typically terminal, thin and wiry, with whitish branches. Branches of the staminate inflorescence typically spreading to lax.

Iresine rhizomatosa inflorescencePistillate inflorescence.

Flowers - Pistillate flowers minute, scarious-white, 1-1.4mm long. Perianth parts scarious-white, acute, ovate, 1.2mm long and broad. Inner 4 parts greenish, lanceolate, acuminate, 1mm long. Ovary superior, green, subglobose, .5mm long and broad, glabrous, 1-seeded. Styles 3, .3-.4mm long, whitish. Staminate flowers minute, whitish, +/-1mm broad.

Iresine rhizomatosa pistillate flowersPistillate flowers.

Iresine rhizomatosa fruits.Fruits.

Flowering - August - October.

Habitat - Low wet woods, thickets near streams.

Origin - Native to U.S.

Other info. - This species can be found in the Ozark region of Missouri. The plant is fairly indistinct vegetatively but is easily identifiable when in flower. The scarious pyramidal inflorescences of the pistillate plants or the thin whitish panicles of the staminate plants are hard to miss in the plants low woodland habitat. The tiny fruits are dispersed by the wind via the tuft of hairs at the base of the flowers and fruits. The plant can be weedy if given the right conditions.

Photographs taken at Shawnee Creek, Shannon County, MO., 9-28-03.


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