Forty-nine species of Mutisieae are presently known from Guayana. They form a closely interrelated group of genera which suggest a history of closed phyletic development and phytogeographically restricted distribution. Of them, only one, Gongylolepis columbiana Cuatr., is extra-Guayanan (occurring in the eastern Andes of Venezuela and Colombia).
Previously to 193lt four members of this assemblage has been recognized, viz., Gongylolepis benthamiana Rob. Schomb.9 Stifftia martiana Baker [Gongylolepis martiana (Bak.) Cuatr. & Steyerm.], Stifftia condensata Baker [Stomatochaeta condensata (Bak.) Mag. & Wurd.], and Ouelchia conferta N. E. Brown. During the period 1931-39, based on specimens collected by Tate, Blake proposed ten additional names (six in Stenopadus, including S. cinereus Gleason & Blake, herein transposed to Chimantaea, and S. variabilis, herein synomized under Stomatochaeta condensata), bringing the total to 13. Now, in the past two decades, contemporary exploration in Guayana has brought to light 36 additional species (and 3 subspecific taxa), of which 14 have been published. Nine are described herein, and 13 are to be treated in the succeeding paper.
During the progress of botanical exploration in Guayana, there has accumulated an impressive and significant body of evidence bearing upon fundamental problems of plant phylogeny, relationships, and geography. Members of the Composite Mutisieae are of special interest in this regard. The following short consideration briefly summarizes arguments which support our interpretation of phyletic derivation and relationship, and hierarchal arrangement of Guayana mutisias. Dr. Sherwin Carlquist has examined our materials anatomically, and has provided a body of data which complements our own. His studies are presented in papers under the titles "Anatomy of Guayana Mutisieae. I. Pollen, and "Anatomy of Guayana Mutisieae. II. Floral Venation" (Mem. N. Y. Bot. Gard. 9:000-000. 1957). Pollen descriptions used in this paper are furnished by Dr. Carlquist.