This species is characterized by its numerous, regularly well developed spinescent short-shoots and lateral stems, opposite rather small leaves often with groups of leaves in each axil, shortly paniculiform inflroescences, 5-merous flowers with small tubular-funnelform corollas, and turbinate fruits. The fruits appear to be at least sometimes indehiscent. Machaonia havanensis was reported from southern Mexico by Lorence et al. (2012), but Borhidi (2012) without explanation did not recognize this species in Mexico. Borhidi's figure (2012:178, fig. 49) is nicely illustrative of the density and sharpness of the spinescent branches of this species. 

Borhidi (2012) recognized two subspecies of Machaonia havanensis in Cuba, with subsp. orientalis found in savannas in a small area of Tunas province. He separated these by disjunct distributions and the leaves pubescent in the typical subspecies vs. glabrous in subsp. orientalis. He synonymized Machaonia calcicola with the typical subspecies; the type of this name has leaves that are glabrous on both sufaces except ciliolate on the margins. The two subspecies are accepted here provisionally, but probably deserve further evaluation as does the synonymy of Machaonia calcicola. 

Machaonia havanensis is known in Mexico and Belize from a few specimens from scattered localities along the Caribbean coast. It was reported only from those Mesoamerican places by Lorence (2012), but review of specimens now shows that the type of Machaonia tysonii from an estuary region in southern Panama matches Machaonia havanensis. This name was synonymized by Lorence et al. (2012) with Machaonia acuminata, based apparently on an annotation by Hamilton, but it differs from Machaonia acuminata by its numerous, rather large, spinescent short-shoots that are regularly developed and relatively small, falcate leaves. This name is here included in Machaonia havanensis and extends the range of this species. The area where this specimen was collected is poorly explored botanically and represents a complicated junction of biogeographic regions. 

The name Spermacoce spinosa Jacq. (1760) has been considered to have been published simultaneously with "Spermacoce havanensis Jacq." (e.g., Borhidi, 2012), but this is inaccurate, because the second name was actually published later by Gmelin (1791). These two names are considered synonymous, and the name Spermacoce spinosa Jacq. has been considered by various authors as an illegitimate later homonym that is blocked by Spermacoce spinosa L. However, Jacquin's name it n fact pre-dates the name Spermacoce spinosa L. (1762), so Jacquin's name is legitimate and in fact Linnaeus cited Jaquin's name in his protologue. Thus the name Spermacoce spinosa has priority over Spermacoce havanensis, but the epithet "spinosa" has been used for another species, Machaonia spinosa Cham. & Schltdl. (1829) so its transfer is blocked and Machaonia havanensis is the oldest available name for this species.