Before comparing these vascular patterns with the remainder of Guayana
Mutisieae composing the basis for this study, a pertinent comparison can be
made with the flowers of Stifftia chrysantha (fig. 106), which is, like Stenopadus,
a South American representative of the subtribe Gochnatinae. The corollas of
this species (fig. 106 A), often have median veins in addition to the lateral veins;
lateral veins do not fuse at the corolla-lobe tips. Median veins, where present,
usually extend only part of the length of the corolla, terminating freely above, and
only infrequently continuing to the base of the corolla tube. As in the vast majority
of Compositae known, though not as in Stenopadus, adjacent laterals fuse beneath
sinuses of the corolla in Stifftia chrysantha. Thus, in the corolla shown, six
bundles enter the achene. In addition to the six bundles in the achene continuous
with those of the corolla, four others are present, forming a total of ten exterior
bundles in the achene wall (fig. 106 C, F). Xylem of stamen traces joins with
that of adjacent corolline bundles in the top of the achene. In the style (fig.
106 B) two bundles are present. These continue into the achene as interior bundles (fig. 106 D, F), but rather than extending to the base of the achene, they join exterior bundles at various points toward the top of the achene (fig. 106 D). Numerous other interior bundles, which terminate freely above, are present in the achene. Together with the ovule trace, these form, in the achene base, a plexus which separates into branches which join exterior bundles below. The ovule trace is unbranched. At the base of the achene, all of the exterior bundles unite into a single strand of vascular tissue which passes into the receptacle.
The floral vasculation of Stifftia chrysantha differs in several features from that of Stenopadus: union of laterals beneath the sinuses of the corolla; union of stylar traces with exterior achene wall bundles near the top of the achene; and union of all achene bundles at the base of the achene to form a single strand. Aside from these features, the venation is not unlike that of Stenopadus, an interesting similarity being the large number of interior bundles present in the achene. The venation of Stifftia uniflora was found to be like that of S. chrysantha, with the exception that no median veins were found in the corolla of S. uniflora.