The Phyllotaxy of Costus (Costaceae)

Publisher Website
Google Scholar
Abstract
The spiromonostichous phyllotaxy of Costus, and other Costaceae, is characterized by low divergence angles, often as low as (30.degree. -) 50.degree.. This contrasts with the main series Fibonacci (divergence angles approximately 137.5.degree.) or distichous phyllotaxy found in all other Zingiberales. A morphological and developmental study of three species of Costus revealed a number of facts about this unusual phyllotactic pattern. In C. scaber and C. woodsonii the divergence angles gradually change along a shoot, from 140.degree.-100.degree. in the region of the cataphylls to 60.degree.-45.degree. in the inflorescence. In C. cuspidatus, the divergence angles change from 40.degree.-100.degree. in the cataphyll region to ca. 137.degree. in the inflorescence. In all three species, the cataphylls and foliage leaves have tubular sheaths, while the inflorescence bracts are nonsheathing. Thus, spiromonostichy is only loosely correlated with closed leaf sheaths.