Trees, shrubs, or herbs (succulent in Pilea), sometimes scandent or epiphytic. Leaves alternate or opposite, petiolate; blades simple, serrate to entire {Pilea), some- times palmately veined at the base; stipules present.
Flowers unisexual (monoecious or dioecious), actinomor- phic, in generally axillary, bracteate cymes or glomerules, sometimes spicate; tepals 3-5, biseriate, undifferentiated (or perianth lacking); stamens 3-5, opposite the tepals, free, springing out elastically at anthesis to throw pollen;
anthers 2-celled, dehiscing longitudinally; ovary superior, 1-locular, 1-carpellate; placentation apical; ovule 1, falsely orthotropous; style and stigma 1; stigma penicillate.
Fruits achenes; seed solitary, with endosperm.
Members of the family are distinguished by the fre- quently stinging trichomes, the minute greenish flowers, and the ovary with one carpel and one style.
Flowers are wind pollinated (Faegri & van der Pijl, 1966). The dry powdery pollen is catapulted by the elastic movement of the stamens at anthesis. G. Frankie (pers.
comm.) reports that in Costa Rica stingless bees may aid in the opening of staminate flowers of Myriocarpa by their persistent probing of unopened flowers.
Dispersal of the minute achenes may be by birds, wind, or water. Boehmeria cylindrica and Myriocarpa yzabalensis usually grow in swampy areas or along water-
40.
URTICACEAE/PILEA363
KEY TO THE SPECIES OF URTICACEAE Leaves opposite, at least along main stem:
Leaves less than 1 cm long, one leaf of a pair ca half the size of the other; blades entire; plants often minute, always less than 30 cm tall Pilea microphylla (L.) Liebm.
Leaves more than 2 cm long, pairs ± equal; blades serrate-dentate; plants more than 50 cm tall Boehmeria cylindrica (L.) Sw.
Leaves alternate:
Flowers in long slender spikes; leaves often more than 8 cm wide Myriocarpa yzabalensis (Donn. Sm.) Killip Flowers not in slender spikes; leaves less than 8 cm wide:
Petioles less than 1 cm long; blades unequal at base Pouzolzia obliqua (Poepp.) Wedd.
Petioles 1-7 cm long; blades ± equal at base Urera eggersii Hieron.
courses, and their seeds may be water dispersed. Pilea microphylla somehow finds itself in every concrete crack in shady areas; possibly its minute seeds are carried around by ants or rain wash. Van der Pijl (1968) reported that in some species of Pilea the staminodia eject the entire fruit.
Some 49 genera with about 2,000 species; widespread but mostly in the tropics.
BOEHMERIA Jacq.
Boehmeria cylindrica (L.) Sw., Prodr. Veg. Ind. Occ.
34. 1788
Monoecious herb, sometimes epiphytic, erect, to 1.5 m high. Leaves opposite on stem, alternate on any branches;
petioles 5-25 mm long, sparsely pubescent; blades nar- rowly ovate or lanceolate, acuminate, rounded to subcor- date at base, 4.5-11 (18) cm long, 2.5-4(7) cm wide, serrate-dentate, glabrous or with inconspicuous pubes- cence on lower surface of veins. Flowers minute, pinkish, in discrete, unisexual, globular clusters along axillary spikes 2-8 cm long and often leafy near the tip; staminate perianth 4-lobed; pistillate perianth 4-toothed, ca 2 mm long, nearly sessile. Achenes ± round, compressed, ca 1 mm diam, brown. Croat 12691.
Uncommon, usually occurring in swampy areas along the shore. Flowers and fruits in the rainy season.
Canada south to southeastern Brazil; West Indies. In Panama, known only from tropical moist forest in the Canal Zone and Bocas del Toro.
See Fig. 208.
MYRIOCARPA Benth.
Myriocarpa yzabalensis (Donn. Sm.) Killip, Proc.
Biol. Soc. Wash. 40:29. 1927 Cow itch
Dioecious shrub or small tree, 3-8 (10) m tall; stems ribbed below petioles, with harsh pubescence. Leaves alternate; petioles one-fourth to as long as blade; blades ovate to ovate-elliptic, abruptly acuminate, mostly rounded at base, 15-40 cm long, 10-25 cm broad, punc- tate, with linear cystoliths conspicuous when dry, glabrous
above, sparsely pubescent on veins below. Staminate spikes to 10 cm long, erect or ± pendent, bracteate, the flowers to 1.2 mm diam; tepals 4; stamens spring flowers open and throw pollen. Pistillate spikes 30-60(90) cm long, slender, pendent; perianth lacking; style oblique on short stalk; stigma brushlike, straight and divergent at anthesis, later curling. Achenes scabrid, ca 1 mm long, soon falling. Croat 4196, 8048.
Frequent along creek banks in the younger forest.
Flowers in the early dry season. The fruits mature in the middle to late dry season.
The achenes are light enough to be blown and prob- ably are carried downstream by water currents. Their scabrid trichomes no doubt play a role in dispersal.
Guatemala to Panama. In Panama, known from tropi- cal moist forest in the Canal Zone, Bocas del Toro, Colon, Los Santos, Panama and Darien, from premontane wet forest in Panama (Cerro Campana), and from tropical wet forest in Darien.
PILEA Lindl.
Pilea microphylla (L.) Liebm., K. Danske Vidensk.
Selsk. Skr. Naturvidensk. Math. Afd., ser. 5, 2:296. 1851
Monoecious (rarely dioecious), glabrous, succulent herb, often minute but to 30 cm high. Leaves opposite, one of each pair smaller; petioles to 2 mm long; blades obovate, mostly obtuse at apex, decurrent at base, the larger to 1 cm long and 5 mm wide, the smaller to ca 3 mm long and
1.5 mm wide, with linear cystoliths. Flowers white, in minute, globular, axillary, ± sessile clusters; stami- nate flowers mostly 4-parted; pistillate flowers usually 3-parted, the middle segment larger than lateral ones.
Achenes ovate, ca 0.5 mm long, brown. Croat 12966.
Locally abundant in shady or moist places in the La- boratory Clearing, especially on sidewalks, concrete, or rock walls; rare elsewhere. Flowers and fruits throughout the year.
Throughout the American tropics. In Panama, known from tropical moist forest in the Canal Zone, Bocas del Toro, Colon, San Bias, and Panama, from premontane wet forest in Code and Panama, and from tropical wet forest in Colon (Portobelo).
POUZOLZIA Gaud.
Pouzolzia obliqua (Poepp.) Wedd., Arch. Mus. Hist.
Nat. 9:405. 1857
Monoecious liana or climbing shrub, to 2(5) m tall; most parts densely hirsute. Leaves alternate; petioles less than 1 cm long; stipules paired, lanceolate, 3-10 mm long, persistent; blades oblong-lanceolate to oblong, acuminate, rounded to subcordate and inequilateral at base, 2-12(15) cm long, 1.5-4.5(5) cm wide, scabrous above with dense punctiform cystoliths. Flowers minute, white or greenish, in small, globular, androgynous (bisexual with staminate flowers at apex) or unisexual clusters; staminate flowers 4-parted; pistillate perianth tubular, 2- or 4-toothed, strongly veined. Achenes ovoid-ellipsoid, acute at apex, 2-4 mm diam, light brown and shiny. Croat 11773.
Occasional, along the shore. Flowers and fruits during the rainy season.
Guatemala to Venezuela and Peru. In Panama, known from tropical moist forest in the Canal Zone, Bocas del Toro, San Bias, Code, and Panama.
See Fig. 209.
URERA Gaud.
Urera eggersii Hieron., Bot. Jahrb. 20, Beibl. 49:3. 1895 Ortiga, Palo ortigo
Dioecious liana or vine, sometimes pendent from trees (elsewhere in Panama sometimes a small tree); young stems densely hirsute, glabrous in age. Leaves alternate;
petioles 1-7 cm long, sparsely pilose; stipules acute, 1.5-2 mm long, caducous; blades ovate-oblong to obovate- oblong (rarely ovate elsewhere), acuminate, obtuse to subcordate at base, 9-17 cm long, 3.5-7.5 cm wide, short- hirsute on veins below or glabrate, entire to obscurely sinuate or crenate-dentate, the linear cystoliths of the upper surface mostly radiating from scattered, pellucid- punctations, those of the lower surface aligned mostly parallel to secondary and tertiary veins. Inflorescences dichotomously branched cymes, 1-5 cm long, about as long as wide; peduncles to 2 cm long, usually less than 1 cm long; peduncles and branches of inflorescence pu- berulent. Flowers unisexual, minute, white or greenish, inconspicuous; staminate flowers 4- or 5-parted, sessile, in glomerules; pistillate flowers 4-parted, usually solitary, short-pedicellate, the style very short, the stigma ± capitate, densely pubescent. Achenes ± globular, to ca 3 mm diam, orange, partially covered by fleshy, enlarged perianth. Croat 12179.
Uncommon, in the forest. Flowers in the late dry and early rainy seasons, from April to September, especially in July and August. The fruits mature mostly from Sep- tember to December, but sometimes in the early dry season.
Possibly several species are involved. In the Flora of Panama (Killip, 1960), this species was treated as U.
elata Griseb., which is endemic to the West Indies. Urera