The Urticaceae are monoecious or dioecious herbs or infrequently shrubs or small trees comprising 45 genera and 700 species, often with specialized stinging hairs. The leaves are alternate or opposite, simple, and almost always stipulate. The minute, unisexual flowers are in cymose clusters. The perianth is of mostly 4 or 5 undifferentiated tepals or is sometimes absent. The male flowers have a stamen opposite each perianth segment. The female flowers have a single simple pistil with a superior or inferior ovary that contains one basal ovule in its solitary locule. The stigma is brushlike and elongated or is capitate. The fruit is an achene or drupe; in a few species these coalesce to form a multiple.
Each "thumbnail" image below is linked to a larger photograph.
||Boehmeria grandis, false nettle, 'akolea, endemic. Exserted stamens are visible in some of the male flowers in the enlarged image at the right.|
|Boehmeria sp. Note cystolith in lithocyst of leaf. These "cyst stones" are of common occurrence in the family.|
||Cecropia obtusifolia, trumpet tree, guarumo. 1, - habit; 2, - canopy, 3, shoot apex, note large, sheathing stipule, 4 - male inflorescences 5 - female inflorescences.|
|Neraudia melastomifolia, ma'aloa. Each female flower has a single, conspicuous, brush-like stigma.|
|Neraudia ?melastomifolia, ma'aloa, male plant, Mt. Ka'ala, O'ahu.|
||Pilea microphylla, artillery plant. Numerous clusters of tiny greenish female flowers are visible. Though not very apparent, each has a tiny stellate-capitate stigma. Two larger, pinkish, unopened male flowers are visible. These have four perianth segments (each with an opposing stamen).|
|Pipturus albidus, mamaki. Mamaki is one of the native Hawaiian species important as a source of fibers. The male plant in the left photo has clusters of tiny staminate flowers. The staminate flowers (middle photo) have a 4-parted perianth with a stamen opposite each segment. A cluster of female flowers is shown in the photo on the right. Note the single, brushlike, elongated stigma on each pistil.|
|Touchardia latifolia, Urticaceae, olona, endemic to Hawaii. Note the 5-merous male flowers.|
|Urera glabra, Urticaceae, opuhe, hopue, hona, Hawai'i Volcanoes National Park, Hawai'i, endemic.|
|Urtica dioica, stinging nettle, vic. Alsea Falls, OR, 2002.|
||Urtica sp., nettles, Aussois, France. Note the tiny greenish flowers and stinging hairs.|
Plant Family Access Page