Cytological and Nomenclatural Notes on the Mesoamerican Species of Aciotis (Melastomataceae)

Abstract

A review of the Mesoamerican species of Aciotis is presented to facilitate the transfer of Spennera alata, an earlier name for the largely Central American species heretofore known as A. levyana. Original chromosome counts of n = 30 are reported for two species, A. alata and A. rostellata, together with brief descriptions, distributional notes, and a regional key to the three Mesoamerican species. Based on a preliminary evaluation of reported chromosome counts, x = 10 appears to be the probable base chromosome number of Aciotis. Aciotis is one of about 30 capsular-fruited genera of the tribe Melastomeae (incl. Tibouchineae) restricted to the Neotropics. This natural genus of herbs and subshrubs is readily distinguished by its small 4-merous flowers borne in terminal panicles, terete hypanthia, eight unappendaged stamens, bilocular ovary, and reniform-cochleate seeds with a foveolate or costate-foveolate testa. Because macromorphological differences among the approximately 30 recognized species (Mathies, 1981) are not always as sharp or as consistent as those encountered in other neotropical genera of the tribe, Aciotis has the reputation of being a taxonomically difficult genus (Wurdack, 1973). Recently, Mathies (1981) contributed to an evaluation of species limits, but the genus is still in need of a thorough field-oriented revisionary study. Despite taxonomic difficulties, identity of the three described species of Aciotis from the Mesoamerican region has not been a major source of confusion. However, examination of type specimens and verification of the identity of taxonomic synonyms pertinent to a treatment of the genus for Flora Mesoamericana has brought to light the need for a new combination that has heretofore been overlooked. Spennera alata, therefore, is transferred here to Aciotis and a synopsis of the three Mesoamerican species is provided together with a key, original meiotic chromosome counts for two of the taxa, and a discussion of the probable base chromosome number of the genus. CHROMOSOME NUMBERS OF ACIOTIS Gametic chromosome numbers are reported here for two populations each of A. alata and A. rostellata. Meiosis was regular with n = 30 in all cells examined from each of these populations. Bud material for these counts was collected from natural populations in the field, fixed in modified Carnoy's solution (4 chloroform, 3 ethanol, 1 glacial acetic acid, v/v/v) for 24 hours, transferred to 70% ethanol, and stored under refrigeration. All counts were made using a Zeiss light microscope with phase contrast and a 100x oil immersion objective. Drawings of meiotic figures were made with camera lucida at a magnification of 2100x. Voucher collections for each of the counts reported here are as follows: Aciotis alata (Beurling) Almeda. n = 30 (Figs. 1, 2). Costa Rica. Lim6n: Forest Reserve at Agricultural College of the Humid Tropical Region ca. 11 km NE of the Guapiles/Lim6n Hwy. at a point 20 km SE of Guapiles, 250 m, 11 Feb. 1992, Almeda et al. 6953 (CAS, CR). Panama. Panami: Cerro Jefe, along summit road and along trail into the Chagres valley, 900 m, 19 Feb. 1988, Almeda et al. 5836 (CAS, PMA). Aciotis rostellata (Naudin) Triana. n = 30 (Figs. 3, 4). Panama. Cocl6: beyond La Mesa on road to the base of Cerro Gaital, 900-1100 m, 23 Feb. 1988, Almeda et al. 5884A (CAS, PMA). Panama. Cocl6: slopes above El Cop6 along abandoned trail to Continental Divide, 700-850 m, 24 Jan. 1989, Almeda et al. 6379 (CAS, PMA). The chromosome count of n = 30 reported here for two Panamanian populations of A. rostellata confirms an identical report for a Costa Rican population of this species by Solt and Wurdack (1980). This same gametic number, which is also reported here for Costa Rican and Panamanian populations of A. alata, is a new number for this species. Solt and Wurdack (1980) reported 2n = 24 for this species (as A. levyana) from Costa Rican seedling maNovoN 7: 333-337. 1997. This content downloaded from 207.46.13.147 on Fri, 20 May 2016 07:56:51 UTC All use subject to http://about.jstor.org/terms