Morphology and Taxonomy of Arcytophyllum serpyllaceum (Rubiaceae), a Transfer from Hedyotis

Abstract

outline, and with a central punctiform hilum. The seeds as shown by scanning electron microscopy are very similar to those of Arcytophyllum muticum (Weddell) Standley, a prostrate, suffruticose species of Costa Rica, Panama, and South America. Seeds of Hedyotideae have been found to be very important in classification (Terrell, 1996). Seeds of Houstonia are crateriform and the hilum is on a hilar ridge (Terrell, 1996), whereas seeds of Hedyotzos serpyllacea are non-crateriform (without ventral depressions or cavities) and lack hilar ridges. Oldenlandia seeds are trigonous or conical and usually much smaller than those of the other genera. Hedyotis as presently recognized includes a heterogeneous array of species, as previously pointed out (Terrell, 1996). I have examined seeds of all of the Western Hemisphere species of Hedyotis, as well as those of many of the Asian species including the type, H. fruticosa L., and all of these seeds differ from those of Hedyotis serpyllacea. A systematic treatment of Arcytophyllum serpyllaceum (Hedyotis serpyllacea) is presented here. This extends the distribution of Arcytophyllum from Panama and Costa Rica into Guatemala and southern Mexico, and also records the first collection of H. serpyllacea in Oaxaca (first noticed by Robert King, cited as Terrell & King 4441).