Morphology and Taxonomy of Arcytophyllum serpyllaceum (Rubiaceae), a Transfer from Hedyotis Edward E. TerrellNorton-Brown Herbarium, H. J. Patterson Hall, University of Maryland, College Park, Maryland 20742-5815, U.S.A.ABSTi\:IT. Morphological and distributional dataare presented for Hedyotis serpyllacea, native toGuatemala and southern Mexico. The species istransferred to Arcytophyllum, extending the rangeof the genus northward from Costa Rica, Panama,and South America. The relationships of the Mexican and Guatema-lan species Hedyotis serpyllacea Schlechtendahl(Rubiaceae; Hedyotideae) have been problematicalfor some years. Its flowers, fruits, and seeds are notsimilar to those of Houstonia (Terrell, 1996), Old-enlandia, or Hedyotis. In 1893 the species was giv-en the name Mallostoma shannonii Donnell Smith,and later Standley transferred it to Arcytophyllum.Morphological data demonstrate that Standley wascorrect in placing it in Arcytophyllum; however, anew combination is necessary. Mena (1990), in a revision of ArcytophyllumWilldenow ex Schultes & Schultes f., recognized 15species native to higher elevations in Costa Rica,Panama, and the Andes of Venezuela, Colombia,Ecuador, Peru, and Bolivia. Eleven species areerect subshrubs and four are prostrate, mat-form-ing, and suffruticose. Mena (1990) listed the nameArcytophyllum shannonii (Donnell Smith) Standleyamong "Excluded and Dubious Names" as a syn-onym for Hedyotis serpyllacea. Hedyotis serpyllacea grows at high elevations(1500 to 3500 m) in Guatemala and southern Mex-ico (Oaxaca, Veracruz, and Chiapas) and has sev-eral vegetative and reproductive morphologicalsimilarities to species of Arcytophyllum. The plantsare prostrate, mat-forming, and suffruticose; thestems have a "jointed" appearance; the stipules aregenerally similar to those of Arcytophyllum; theleaves are small, rather thick, and leathery; the ca-lyx has intercalycine teeth; the corollas are ratherthick, purplish externally and white within; and thecapsules are broadly oblong, thick-walled, and tar-dily dehiscent. All of these characteristics occurespecially in the prostrate, suffruticose species ofArcytophyllum, to which H. serpyllacea is mostclosely allied. Seeds are compressed, rounded inoutline, and with a central punctiform hilum. Theseeds as shown by scanning electron microscopyare very similar to those of Arcytophyllum muticum(Weddell) Standley, a prostrate, suffruticose speciesof Costa Rica, Panama, and South America. Seeds of Hedyotideae have been found to be veryimportant in classification (Terrell, 1996). Seeds ofHoustonia are crateriform and the hilum is on ahilar ridge (Terrell, 1996), whereas seeds of Hedy-otis serpyllacea are non-crateriform (without ventraldepressions or cavities) and lack hilar ridges. Old-enlandia seeds are trigonous or conical and usuallymuch smaller than those of the other genera. Hed-yotis as presently recognized includes a heteroge-neous array of species, as previously pointed out(Terrell, 1996). I have examined seeds of all of theWestern Hemisphere species of Hedyotis, as well asthose of many of the Asian species including thetype, H. fruticosa L., and all of these seeds differfrom those of Hedyotis serpyllacea. A systematic treatment of Arcytophyllum serpyl-laceum (Hedyotis serpyllacea) is presented here.This extends the distribution of Arcytophyllum fromPanama and Costa Rica into Guatemala and south-ern Mexico, and also records the first collection ofH. serpyllacea in Oaxaca (first noticed by RobertKing, cited as Terrell & King 4441).Arcytophyllum serpyllaceurn (Schlechtendahl) Terrell, comb. nov. Basionym: Hedyotis serpyl-lacea Schlechtendahl, Linnaea 9: 599. 1834. Houstonia serpyllacea (Schlechtendahl) C. L. Smith ex Greenman, Proc. Amer. Acad. Arts 32: 284. 1897. TYPE: Mexico. Veracruz: be-tween La Joya and San Salvador, June 1829, Schiede 265 [Deppe's name was not included with Schiede's] (holotype, HAL; isotypes, F, HAL, MO; photos taken at B are at F, GH, MO, NY, US; however, the B specimen was destroyed during World War II).Mallostoma shannonii Donnell Smith. Hot. Gaz. (Craw-fordsville) 18: 203. 1893. Arcryoh lnIlumrn shannonii (Donnell Smith) Standley, Contr. U.S. Natl. Herb. 18: 128. 1916. TYPE: Guatemala. (himaltenango: NOvN 9: 263-264. 1999.
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