Spermacoce ferruginea St. Hil., Pl. Usuell. Bras. pl. 13. 1824.
Borreria ferruginea (St. Hil.) DC., Prodr. 4: 547. 1830.
Borreria kappleriana Miq., Symb. Surin., Linnaea 18: 746. 1844.
Borreria nectarifera Rusby, Mem. N. Y. Bot. Gard. 7: 381. 1927.
Spermacoce ferruginea St. Hil. was described and illustrated with leaves “lanceolatis vel lanceolato-ovatis, lanceolatove-oblongis” and stems “pubescente,” the upper leaf surface scarcely pubescent, the lower surface with a little pubescence and with a width of “4 a 5 lignes” [9.2-11.5 mm]. This is similar to shape and size of leaves of Spermacoce capitata R. & P. (= Borreria capitata) from Peru, but differing in the greater amount of pubescence on stems and leaves, and with the additional difference of spreading hairs on the stem. Luschnath 94, identified as Borreria ferruginea in the Martius Herbarium no. 598, from Cruz de Casma, prov. Soteropolitana (Edo. Bahia), July 1839, has oblong-elliptic leaves, the broadest ones 14-16 mm, with the leaf blades more or less moderately short pubescent above, but with longer and more pilosulous pubescence beneath on the nerves and shorter, more sparse pubescence on the lower surface. Blanchet s n from Bahia, Brazil, is similar to the Luschnath 94 specimen with conspicuous spreading pubescence. Specimens agreeing with the description and plate of Spermacoce ferruginea, as well as coming from the region of the type locality, are: Luerderwaldt 11860 from Ipiranga, Sao Paulo; Ball s n “ex apricis Brasiliae juxta São Paulo”; Irwin 2211 from Vicosa, Minas Gerais; Mexia 4824 from Vicosa, Minas Gerais. These all agree with B. ferruginea in having a dense abundance of spreading short hairs on the stems and with lanceolate- or oblong- to ovate-elliptic leaves 7-10 mm broad.
Although the leaves of Borreria ferruginea are typically broadest in the middle with an elliptic or lanceolate- to oblong-elliptic shape, variations exist with cauline leaves oblanceolate or linear-lanceolate to lanceolate, with sides more parallel and not broadest in the middle. Since the more parallel-sided leaves grade gradually in some specimens to leaves broadest above the base or at the middle, it has not been possible to separate such intergradations with densely pubescent leaves and stems, and all have been placed under forma ferruginea. Moreover, this abundantly pubescent variation grades into the typical form of B. capitata with less pubescence, and can be considered merely a more pubescent form of the taxon. Like typical B. capitata, the densely pubescent-stemmed and broader-leaved pubescent f ferruginea possesses transversely sulcate seeds.