Abstract
D. schuetzei Rolfe, D. sanderae Rolfe and P. dearei Rolfe, endemic to the Philippines have 20 pairs of chromosomes, while D. draconis Rchb. f., and D. formosum Rchb.,from southern Asia have 19 pairs. The chromosomes of D. formosum are about twice the size of those of D. sanderae. Those of D. draconis are intermediate in size. Complete chromosome pairing in interspecific diploid hybrids of the Philippine group is conclusive evidence of their close phylogenetic relationship. The triploid hybrid D. sanderae x D. dearei forms 13-19 trivalents, and 1-7 bivalents and univalents. D. dearei x D. formosum with 39 chromosomes, has 11-19 bivalents, mostly heteromorphic. The results suggest the Philippine species are more closely related to each other than to the extra-Philippine species.

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