Borreria capitata (R. & P.) DC., Prodr. 4: 545. 1830.
Borreria tenella var platyphylla Schum., Mart. Fl. Bras. 6(6): 55. 1888.
Spermacoce capitata R. & P., Fl. Peruv. 1: 61, pl. 91, fig b. 1798.
The specimens from the Guianas and Venezuela cited above are essentially the same or similar to the typical peruvian material of Borreria capitata, of which I have seen type material from (1) a fragment of the type from MA at F, and (2) a specimen on the left hand side of the sheet at the Fielding Herbarium of Oxford, attached to which is a note, signed by Dr. John Richards, Curator, in 1968, that “This is collected by Ruiz and Pavon according to Clokie, as the handwriting is the same as for their S. corymbosa." In both the specimens at Field Museum and at Fielding Herbarium, the stems are sparsely appressed-pubescent in lines (in the Fielding Herbarium plant), but more uniformly appressed-pubescent in the specimen at Field Museum, the stipular awns are 5-6 mm long, and mainly glabrous from base to apex, the stipular sheath is minutely and uniformly pubescent with densely appressed puberulence, and the leaves are shortly appressed-hispidulous above, more abundantly near the base, but sparsely pubescent elsewhere, and below are glabrate on the surface but hispidulous with appressed hairs, whereas on the midrib and lateral nerves beneath the hairs are chiefly spreading. The heads are best developed in the Fielding Herbarium specimen, depressed hemispheric, and 8-10 mm high by 15-16 mm broad. The calyx lobes in the type material are 4 to a flower, linear, pale margined, acute to acuminate, glabrous except for the hispidulous-ciliolate margins, and 2.5-2.8 × 0.2-0.3 mm. In the Fielding Herbarium specimen the subtending involucral leaves are reflexed, four in number with two larger and two smaller, the larger lanceolate, acute, sulcate-nerved above, 23 × 4.5 mm, shortly appressed-hispidulous above and rather sparsely so, except more abundantly at base, hispidulous below on the midrib and lateral nerves, but glabrate on the surface.
The specimens of Ruiz and Pavon represent a lightly pubescent variation of the Borreria capitata complex, but other Peruvian material shows variations from glabrate stems and glabrate lower leaf surface to stems more densely pubescent with degrees of denser pubescence on the lower and upper leaf surfaces. I have taken these more glabrate types as corresponding to and matching the Ruiz and Pavon material. Thus, the material cited above from the Guianas, Venezuela, and Brazil most closely matches the peruvian specimens cited. The following notes indicate the similarities and slight differences within the range of variation of typical B. captata: in the material from the Guianas, etc., cited above the stems are usually retrorsely pilose on the angles and sparingly appressed-puberulent on the faces between the angles or glabrescent. Usually the upper leaf surface is completely glabrous as contrasted with shortly and minutely sparsely appressed-pubescent upper surface of the peruvian material, while the lower surface of the leaf in the Guiana, etc. material is generally glabrous, although sometimes sparse appressed hairs are present, and the lateral nerves and midrib of the lower side of the leaf are usually villous or hirsutulous with longer, denser, and more spreading hairs than in the peruvian material. Instead of usually 3-4 pairs of lateral nerves on each side of the leaf blade, as in the peruvian type material, the specimens cited from the Guianas, etc. show 4-7 lateral nerves on each side (often 6-7), and are usually prominently sulcate-nerved above. Likewise, mature seeds are transversely sulcate in both the peruvian material as well as in that from the Guianas, etc. It is difficult, and scarcely of taxonomic significance, to draw any arbitrary divisions of categories between the extremes with the upper leaf surface completely glabrous, as in those on the Guianas, etc., and those with pubescence on the upper surface, or, moreover, to separate those having shorter and more scattered, subappressed to ascending hairs from others in which the hairs are longer, denser, and more spreading. Therefore, I am treating, at least tentatively, typical B. capitata as representing a series of variations, allowing for extremes of glabrity and pubescence on the upper leaf surface, as well as of degrees of density of pubescence on the midrib and lateral nerves of the lower side.