8. Spermacoce L.

About 30–250 species (depending on generic circumscription), in the broad sense nearly worldwide.

The genus Spermacoce has been delimited in several very different ways. There is much variation in the fruits of the group, and this has been given differing weights by various authors. In general Spermacoce and its relatives are herbs and low shrubs with bristly stipules and 2-seeded, small, dry fruits. Diodia of our flora is related; this genus is distinguished by its fruits that split into two parts, with each part indehiscent, and is native to the New World. About 100 other species found in tropical and warm-temperate regions around the world are similar to Diodia, but have fruits that dehisce to some extent, or sometimes do not dehisce or split apart at all. Some authors, led by Verdcourt (1958, 1976) and Fosberg et al. (1993), have considered the fruit type to be relatively unimportant for classification in this group, and have included all these species in one cosmopolitan genus, Spermacoce. However, other authors, including Steyermark (1963) and Bacigalupo and Cabral (1999), have considered fruit type very important in this group, and have used it along with several other features, especially pollen morphology (which is quite variable among these plants), to separate various genera.

Bacigalupo and Cabral (1999) included in their version of the genus Spermacoce only about 30 New World tropical species with unusual fruits that are asymmetrical, with the larger half opening to release its seed and the smaller half remaining closed (dispersing with its seed still inside). In their classification, the Missouri species of Spermacoce, which does not have this fruit type, was segregated into its own genus, Spermacoceodes Kuntze (although the Caribbean species Tobagoa maleolens Urb. has similar fruits and may be closely related). Until this entire group is better understood through careful worldwide study, the generic classification will not be agreed upon and consequently will continue changing. Therefore, the genus Spermacoce is retained in the traditional sense in the present treatment to include the Missouri species.