Thunbergia Retz.

Daniel, Thomas F., 2018, Chromosome Numbers of Some Cultivated Acanthaceae with Notes on Chromosomal Evolution in the Family, Proceedings of the California Academy of Sciences 64 (9), pp. 319-332 : 328

Thunbergia Retz.

— Thunbergia consists of about 150 species that are native to tropical (and subtropical) regions of the Old World. Our approximate counts for T. erecta (Benth.) T. Anderson (n = ca. 30), native to western tropical Africa and for the white-flowered form of T. grandiflora Roxb. (n = ca. 28), native to southern Asia, generally agree with at least some prior counts for these species. Previously, n = 28 has been reported for T. grandiflora at least six times and n = 14 (or ca. 14) has been reported twice ( Daniel 2000b). In compiling previous counts for T. erecta (i.e., n = 8, 14, 26, ca. 28, 28, 30, 31, and 32), Daniel and Chuang (1998) noted their own difficulties in obtaining definitive counts for this species. They concluded that if previous counts for it are accurate, a diversity of chromosome numbers and ploidal levels are characteristic of the species. Our approximate count of n = 32–34 for the Indian endemic T. mysorensis (Wight) T. Anderson is the first for this species, and would appear to represent a ploidal level similar to the majority of counts for both T. erecta and T. grandiflora .

Chromosome numbers are known for 10 species of Thunbergia . The lowest numbers reported to date are n = 8 (e.g., Govindarajan and Subramanian 1983 for T. erecta ), n = 9 (at least 13 counts: e.g., Daniel and Chuang 1989 for T. alata Bojer ex Sims , e.g., Grant 1955 for T. reticulata Hochst. ex Nees ), and n = 10 (e.g., Sharma 1970 for T. coccinea Wall. ). Multiples of n = 8 and n = 10 are known among species of Thunbergia , and these numbers may represent basic numbers in the genus. Daniel and Chuang (1998) proposed the former as a likely basic number. Unfortunately, chromosome numbers remain unknown for the two most likely generic relatives in subfamily Thunbergioideae , Pseudocalyx Radlk. and Meyenia Nees. From the diversity of numbers reported for the 10 species of Thunbergia studied to date, and considering the variation apparent within some species, it would appear that whatever the ancestral basic number is for this large genus, knowledge of chromosome numbers could be informative in phylogenetic studies of both Thunbergia and its relatives.