Flora of North America species comparison

Acalypha rhomboidea often has been called A. virginica due to controversy about the typification of that name. Conservation of the type of A. virginica resolved the issue. This nomenclatural problem, combined with use of inappropriate characters to distinguish A. rhomboidea and A. virginica, has resulted in considerable confusion between these amply distinct species. The two can be distinguished most readily by the pistillate bracts, which are clearly hirsute abaxially in A. virginica but sparsely pubescent abaxially in A. rhomboidea. In addition, the bracts of A. virginica have (8–)10–14(–16) triangular lobes one fourth to one half the bract length, whereas those of A. rhomboidea have (5–)7–9(–11) lanceolate or triangular lobes one third to two thirds the bract length, and the stems of A. virginica usually are hirsute whereas the stems of A. rhomboidea are rarely so.

In the southern part of its range, many Acalypha rhomboidea plants have been confused with A. gracilens. These plants are more delicate than A. rhomboidea from farther north, with notably smaller pistillate bracts, and they usually produce allomorphic flowers, whereas more robust or northerly plants rarely do. They can be distinguished from A. gracilens by having relatively wider leaves and pistillate bracts with fewer lobes and no red sessile glands.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Species ca. 450 (18 in the flora).

Some species of Acalypha are cultivated as ornamentals, notably A. herzogiana Pax & K. Hoffmann, A. hispida Burman f., and A. wilkesiana; the last has become naturalized in Florida. Acalypha herzogiana has escaped locally on Dauphin Island, Alabama (H. Horne, pers. comm.). It may escape locally elsewhere but might not become naturalized in the flora area, because the cultivated form is sterile, although pieces of the plant root readily if they are spread. It is an herbaceous perennial readily recognized by its erect, feathery, red spikes of sterile pistillate flowers (V. W. Steinmann and G. A. Levin 2011).

Acalypha mexicana Müller Arg. [A. indica Linnaeus var. mexicana (Müller Arg.) Pax & K. Hoffmann], native from central Mexico to Guatemala, was collected twice early in the twentieth century in southeastern Arizona but has not been collected there since and presumably did not become established. It will key here to A. australis; A. mexicana differs in having pistillate bracts that are 10 mm and eglandular (versus 10–15 mm and glandular) and allomorphic flowers that are common, long-pedicelled, and 1-carpellate (versus rare, sessile, and 2-carpellate).

Some Acalypha species, including about half of those in the flora area, produce allomorphic pistillate flowers (A. Radcliffe-Smith 1973). These flowers may be mixed with normal pistillate or staminate flowers or be terminal on the inflorescence. Their pistils generally have fewer carpels than normal pistillate flowers of the same species, bear sub-basal rather than terminal styles, and develop into nutlets or schizocarps, frequently bearing bristles or variously ornamented outgrowths that presumably facilitate dispersal. Unlike normal pistillate flowers, allomorphic flowers frequently lack bracts and are borne on elongate pedicels. Characters of these flowers generally are species-specific and useful for identification (Radcliffe-Smith).

The bracts subtending normal pistillate flowers of most Acalypha species, including all in the flora area, enlarge as the fruits develop. Measurements for these bracts, referred to here as pistillate bracts, and the pistillate portion of the inflorescences given in the key and descriptions are post-anthesis, after the bracts have completed most or all of their growth.

Seed descriptions pertain to those from normal pistillate flowers.

The sequence of species below starts with shrubs (species 1 and 2), followed by subshrubs and perennial herbs (species 3 to 6), and concludes with annual herbs (species 7 to 18). Within each growth form, similar species are grouped together.

(Discussion copyrighted by Flora of North America; reprinted with permission.)