Pilea pumila (L.) A. Gray

Clearweed

Pilea_pumila_plant2.jpg
STATS

Native
CC = 4
CW = -3
MOC = 68

© SRTurner

Family - Urticaceae

Habit - Annual taprooted forb, monoecious or dioecious, unarmed, glabrous, the stems and leaf petioles translucent.

Stem - Stem - To 50 cm, erect or ascending, occasionally from a spreading base, usually unbranched, stout, glabrous, translucent, and slightly succulent.

Pilea_pumila_stem.jpg Stem.

© SRTurner

Leaves - Opposite, long-petiolate, stipulate. Blades 2-12 cm long, elliptic to ovate, glossy adaxially, broadly angled to rounded at the base, tapered at the tip, the margins bluntly toothed to nearly scalloped or occasionally sharply toothed, with 3 main veins; cystoliths linear.

Pilea_pumila_leaf1.jpg Leaves, adaxial.

© SRTurner

Pilea_pumila_leaf2.jpg Leaf abaxial.

© SRTurner

Inflorescence - Small axillary clusters, these often arranged into small panicles, the staminate and pistillate flowers usually on different branches of the same panicle. Bractlets not forming an involucre.

Flowers - Staminate flowers with 4 sepals, these 0.7-1.1 mm long, loosely cupped around the stamens. Stamens 4. Pistillate flowers with 3 free sepals, these 0.8-1.2 mm long, equal or occasionally 1 somewhat enlarged and hoodlike. Style absent, the stigma capitate, not persistent at fruiting.

Pilea_pumila_inflorescence.jpg Inflorescence.

© SRTurner

Fruits - 1.3-1.8 mm long, flattened, ovate in outline, the surfaces smooth, green or straw-colored, sometimes with purplish streaks.

Pilea_pumila_fruits.jpg Fruits.

© SRTurner

Pilea_pumila_fruits2.jpg

© SRTurner

Flowering - July - October.

Habitat - Bottomland forests, margins of streams, ponds, lakes and sloughs, moist disturbed soils.

Origin - Native to the U.S.

Lookalikes - Pilea fontana; more broadly, other members of the Urticaceae such as Urtica dioica and Boehmeria cylindrica; also Acalypha rhomboidea.

Other info. - This small species occurs throughout Missouri and is quite common in the listed habitats. Its range extends across the eastern half of the continental U.S. and into Canada.

Although a member of the nettle family, this species has no stinging hairs and may be handled freely. In appearance it is similar to several other members of the family, but is unique in its succulent, translucent stems and leaf petioles. The see-through stems have been used to demonstrate vascular conduction in plants. A fresh specimen placed in dyed water will draw up the solution, outlining the vascular elements in color.

For differentiation from P. fontana, see the page for that species.

Photographs taken in Weldon Spring Conservation Area, St. Charles County, MO, 8-15-2010, and along the Katy Trail northwest of Dutzow, Warren County, MO, 9-4-2015 (SRTurner).