Cytotaxonomic Notes on Some Neotropical Gentianaceae

Abstract

Chromosome numbers for 13 species in four genera of neotropical Gentianaceae are reported for the first time. The chromosome numbers suggest a relationship between Symbolanthus, Macrocarpaea, and Chelonanthus and support the separation of Lisianthius and Chelonanthus. The Gentianaceae is a moderate-sized family, comprising approximately 800 species (Engler & Diels, 1936). Their distribution is essentially worldwide. In many cases generic limits within the family are poorly defined, and intergeneric relationships are poorly understood. Particularly troublesome are those approximately 100 neotropical members of the family which are supposedly related to Lisianthius P. Browne. In accordance with the genera accepted by Gilg (1895) this would include the following: Macrocarpaea Gilg, Pagaea Griseb., Helia Mart., Irlbachia Mart., Lehmaniella Gilg, Adenolisianthus Gilg, Calolisianthus Gilg, Chelonanthus Gilg, Purdieanthus Gilg, Lagenanthus Gilg, Rusbyanthus Gilg, Symbolanthus Don, and Lisianthius P. Browne. Taxonomic studies of this group of genera have been hampered not only by the paucity of specimens, but also by their miserable condition. Macrocarpaea is the only genus of moderate size for which a reasonably complete monograph (Ewan, 1948) is available. With the exception of Gentiana and its segregates, little is known about the cytology of the family. There are apparently no published chromosome counts for any of the lisianthioid genera. Counts are reported here for the first time for thirteen species in four of the genera. The standard squash technique was used: Flower buds were fixed in modified Carnoy's solution, stored in 70% ethanol, and the pollen mother cells were subsequently squashed in acetocarmine. The results are listed in Table 1. According to the most comprehensive treatment of the Gentianaceae (Gilg, 1895), Lisianthius and Macrocarpaea belong to the tribe Gentianeae, subtribe Tachiinae, while Chelonanthus and Symbolanthus belong to the tribe Helieae. In Gilg's treatment the Gentianeae and the Helieae, as well as most other major groupings within the family, were delimited on the basis of pollen grain morphology. Those genera whose pollen grains are united into tetrads were referred to the Helieae; all other genera supposedly are characterized by having separate pollen grains. The findings of more recent authors suggest that Gilg's system is probably inadequate. Ewan (1948) argued that the genera most closely related to Macro'Most of the field work involved in this study was supported by National Science Foundation Grant GB-6393. I thank Dr. Robert L. Wilbur and Dr. Donald E. Stone for assistance in the preparation of this manuscript. Cytological vouchers are in DUKE. 2Department of Botany, Duke University, Durham, North Carolina 27706. ANN. MISSOURI BOT. GARD. 56: 439-443. 1969. This content downloaded from 157.55.39.243 on Wed, 05 Oct 2016 04:40:20 UTC All use subject to http://about.jstor.org/terms