[1][2][3] The genus name Acalypha is from the Ancient Greek ἀκαλύφη (akalúphē) ("nettle"), an alternative form of ἀκαλήφη (akalḗphē),[4] and was inspired by the nettle-like leaves.

Native North American species are generally inconspicuous most of the year until the fall when their stems and foliage turn a distinctive coppery-red.

Male flowers very small, shortly pedicellate, globose in bud; calyx parted into 4 small valvate sepals; stamens 4–8(–16) on a slightly raised receptacle, filaments free or basally connate; anthers with divaricate or pendulous thecae, unilocular, more or less elongated and later becoming vermiform; pollen grains oblate-spheroidal, with 3–5 pseudopores, tectate, psilate; pistillode absent.

Female flowers generally sessile or subsessile, pedicellate in a few species; calyx of 3– (4–5) small sepals imbricate, connate at base; ovary of [1–2]3 carpels, surface often muricate, pubescent or papillose; ovules solitary in each cell, anatropes; styles reddish, free or basally connate, several times divided into filiform segment, rarely bifid or entire; staminodes absent.

Seeds small, ovoid or ellipsoid, usually carunculate, smooth or foveolate; endosperm present, whitish; the embryo straight; cotyledons broad and flat.

[8] The genus Acalypha was described in the Species Plantarum by Linné (1753), as belonging to the monoecia monadelphia class along with other Euphorbiaceae genera such as Croton, Jatropha and Ricinus.

In the same year, Nikolaus Joseph von Jacquin, as a result from his journey to Caribbean Sea, writes Enumeratio Systematica Plantarum, in which species A. villosa and A. carthagenensis from Colombia, and A. corensis from Venezuela are described.

[8] In the French botanist Henri Baillon publication Étude générale du groupe des Euphorbiacées (1858), a large morphological description of genus is made, and a peculiar classification is presented: two sections are considered –“Sect.

As a preparation for that public book, he published in Flora journal a lot of descriptions of new species based on specimens of Hooker herbarium, at Kew Gardens (Müller Argoviensis, 1864).

In such a work, Müller for the first time uses a classification of Acalypha in two sections, i. e. “Linostachys” and “Euacalypha”, names which accompany each of the described species.

In 1865, he publishes in Linnaea journal a first revision of genus, in which 164 species are gathered –67 of them first time described– and Acalypha is formally divided into two sections as above referred.

The Linostachys section is based on the homonymous genus from Klotzsch (1846), and includes seven species with pedicellate male flowers and bracts non-increasing in the fruit.

This latter section is in turn divided into “series”, “subseries”, and finally in groups designated by the symbol “§”, mainly according to the relative positions of male and female flowers in inflorescences and depending on whether these are axillary or terminal, unisexual or bisexual.

We must highlight the work from John Hutchinson (1913) for Flora of Tropical Africa by Thiselton-Dyer, where he is dealing with 42 species in modern flower format and, for the first time, he introduces a dichotomous identification key.

[8] In a general paper on Euphorbiaceae systematics, Isao Hurusawa (1954) sets forth a new classification, where the rank of infrageneric taxa is even raised and a proposal is made to divide Acalypha into seven subgenera with 19 sections.

Grady Webster (1967), in a study of Euphorbiaceae genera from Southeastern USA, deems inadequate the treatments given by Pax & Hoffmann and Hurusawa; he thinks that by dividing genus into two sections with many infrasectional taxa, such as presented by Müller, the grade of kinship between Acalypha species seems to be better outlined.