Iresine rhizomatosa Standl.



CC = 5
CW = -3
MOC = 43

© DETenaglia

Family - Amaranthaceae

Habit - Perennial forb, dioecious, with slender rhizomes.

Stems - Ascending to erect, to 1.5 m, multiple from the base, somewhat angled or slightly ridged longitudinally, inconspicuously pubescent with short, unbranched hairs, often only at the slightly swollen nodes.

Iresine_rhizomatosa_stem.jpg Stem and node.

© DETenaglia

Leaves - Opposite, simple, petiolate. Petioles to 5 cm long, winged by decurrent leaf tissue, reddish at the base, glabrous. Blades 5-14 cm long, thin and herbaceous, lanceolate to more commonly ovate, tapered abruptly at the base, gradually narrowed or tapered to a sharply pointed tip, the margins entire or occasionally minutely and sharply toothed, the surfaces glabrous or sparsely and inconspicuously pubescent with unbranched hairs, the undersurface sometimes appearing pebbled when dry.

Iresine_rhizomatosa_leaves1.jpg Leaves, adaxial.

© SRTurner

Iresine_rhizomatosa_leaf2.jpg Leaf, abaxial.

© SRTurner

Iresine_rhizomatosa_leaves.jpg Pressed leaves.

© DETenaglia

Inflorescence - Terminal, and sometimes also axillary, pyramidal panicles with numerous short spikes along the ultimate branches, those of staminate plants usually with more spreading branches than those of pistillate plants. Bracts similar in texture but somewhat shorter than the sepals, papery or scalelike, glabrous. Flowers sessile, only slightly overlapping, the axis clearly visible between the individual flowers.

Iresine_rhizomatosa_inflorescence.jpg Staminate Inflorescence.

© SRTurner

Iresine_rhizomatosa_inflorescence2.jpg Inflorescence detail.

© SRTurner

Flowers - Imperfect, the pistillate ones with dense, long, woolly to cobwebby hairs at the base. Sepals 5, free or rarely fused only at the very base, all similar in size and shape, 1.2-1.5 mm long, narrowly ovate, narrowed to a bluntly or sharply pointed but unawned tip, papery or scalelike, not becoming hardened after flowering, silvery white, glabrous. Staminate flowers with 5 stamens, the filaments fused toward the base, usually alternating with 5 minute, triangular teeth, sometimes a highly reduced rudimentary pistil also present. Pistillate flowers with the ovary superior, green, oblong to nearly circular in outline, flattened (elliptic in cross-section), sometimes with 5 highly reduced staminodes present. Ovule 1. Style absent or very short, persistent, the stigmas 2, slender.

Iresine_rhizomatosa_pistillate_flowers.jpg Staminate flowers.

© DETenaglia

Fruits - Achene-like fruits with papery walls, 2.0-2.5 mm long, more or less circular in outline, flattened, more or less rounded at the tip, minutely beaked, glabrous, indehiscent, 1-seeded. Seeds 0.4-0.6 mm long, more or less globose, the surface reddish brown to black, shiny.

Iresine_rhizomatosa_fruits.jpg Fruits.

© DETenaglia

Flowering - August - October.

Habitat - Bottomland forests, particularly near streams, streambanks, bases of bluffs, disturbed shaded areas.

Origin - Native to the U.S.

Other info. - This species is found in Missouri almost exclusively in counties south of the Missouri River. Beyond Missouri its range extends mostly southward to the Gulf Coast. Most of the plant's populations are found within 7-8 states. When flowering it is an easily recognized species, with typically large, whitish inflorescences. It is almost always found in moist, shaded bottomlands near rivers. The tiny fruits are dispersed by the wind via the tuft of hairs at the base of the flowers and fruits.

Photographs taken at Shawnee Creek, Shannon County, MO., 9-28-03 (DETenaglia); also at Shaw Nature Reserve, Franklin County, MO, 9-4-2011, and Onondaga Cave State Park, Crawford County, MO, 9-25-2014 (SRTurner).