Rockweed

The “gunpowder” or “Artillery plant”, a native of tropical America, is widespread in tropical and subtropical regions throughout the world. It is commonly cultivated in pots in gardens.

Pilea microphylla has been collected once in Tennessee and once in Michigan, but it is unlikely that the species persists so far north. It is widely grown as a houseplant in the north and a border plant in the south. It is a greenhouse weed in various parts of the flora.

Annual or biennial, prostrate or procumbent suberect, fleshy, glabrous herb. Leaves anisophyllous, with filiform, 2-3 mm long petiole; lamina obovate, elliptic or suborbicular, up to 10 mm long and 6 mm broad, entire, cuneate at the base, obtuse; stipules minute. Inflorescence of axillary compact, globose flower clusters. Flowers yellowish green. Sepals ovate, acute. Achenes oblong.

Herbs , annual or short-lived perennial, 0.3-2 dm. Stems 10-40-branched, erect. Leaf blades spatulate to obovate, paired blades unequal, the larger 3-10 × 1.5-5.5 mm, the smaller 1.5-4 × 0.7-2 mm, margins entire. Inflorescences crowded. Flowers ca. 0.5 mm across. Achenes uniformly light brown, slightly compressed, ovoid-cylindric, ca. 0.5(-1.1) × 0.3 mm, smooth.

Herbs weak, glabrous, monoecious. Stems erect or ascending, blue-green when dry, simple or branched, 3-17 cm tall, 1-1.5 mm in diam., succulent, cystoliths dense. Stipules persistent, triangular, ca. 0.5 mm, membranous; petiole slender, unequal in length, 1-4 mm; leaf blade abaxially pale green, adaxially green, obovate or spatulate, unequal in size, 2-7 × 1.5-3 mm, succulent, papery when dry, midvein indistinct distally, lateral veins several, indistinct, abaxial surface honeycombed, cystoliths linear, adaxial, regularly transverse, base cuneate or attenuate, margin entire, somewhat recurved, apex obtuse. Inflorescences often androgynous, compactly cymose-capitate; peduncle 1.5-6 mm, sometimes sessile; glomerules few flowered. Male flowers pedicellate, ca. 0.7 mm; perianth lobes ovate, subapically corniculate; rudimentary ovary minute, conic. Female perianth lobes subequal, oblong, longer lobe subequal to achene. Achene ovoid, ca. 0.4 mm, compressed, smooth, enclosed by persistent perianth. Fl. Jun-Aug, fr. Sep-Oct.

Distribution: Tropical America, Africa, Asia and Eastern Europe.

Fla., Ga., La., S.C.; Mexico; West Indies; Central America; tropical South America; Pacific Islands (Hawaii); Asia.

FI.Per.: March-August.

Flowering all year.

Waste places, hammocks, rocky woods, cultivated plots, on masonry; 0-100m.

Commonly naturalized in S China and in greenhouses in N China [native to tropical South America].

Parietaria microphylla Linnaeus, Syst. Nat. ed. 10, 2: 1308. 1759

Parietaria microphylla Linnaeus, Syst. Nat., ed. 10, 2: 1308. 1759.