Anatomical features by which O. ptaritepuiana may be differentiated from O. sceptrum include relative lignification of the central portion of the stem; thickness, epidermal sclerification and shape of bundles in leaves; distribution of parenchyma in the sepals; size and sexine ornamentation of pollen grains.
The closest relationships among genera of Xyridaeeae is that between Abolboda
and Orectanthe. Segregation of the latter genus is well deserved, however.
Orectanthe has larger stems with a distribution of selerenchyma different from
that in Abolboda. Orectanthe has more bundles in its leaves, more bundle-sheath
extensions, a tendency towards abaxial hypodermis production, and no thornlike
leaf-tip with peculiar tracheids. It has spongy chlorenchyma and lignified
bundle sheaths in the cortex of the inflorescence axis. It has distinctive sepal
size and anatomy, and the inflorescence-axis bract is notably lacking in selerenchyma
or other differentiation. Orectanthe lacks staminodia, has more elaborate
corolla venation, and a massive anther connective. Capsule-valve anatomy and
especially seed anatomy provide excellent characteristics to distinguish the two
genera. Pollen morphology provides an exemplary instance of a generic degree
of distinction between Abolboda and Orectanthe.
Achlyphila could probably be defined, on the basis of present knowledge, on
a number of anatomical features. The root offers peculiar endodermis characters
and vessels well toward the interior of the core, which, however, lacks central
vessels. The stem shows modifications corresponding with its rhizomatous habit,
such as a stem endodermis. The leaves have a peculiar equitant habit, and the central core of lignified parenchyma in upper portions is peculiar. The flattened inflorescence axis, lacking- veins in the "pith" region, is distinctive. Sepal anatomy could be used to separate Achlyphila from the other genera, and floral venation reveals both a lack of staminodia and a choripetalous condition. Pollen is peculiar because it combines a peculiar patch-like presence of long pila with a lack of major ornaments and a nonaperturate condition.
Detailed comments cannot be made on Xyris, because it has been excluded from this study. Such characteristics as lack of '' pith'' bundles in the inflorescence axis, distinctive seed anatomy, and the peculiar nature of the monosulcate pollen provide features which, as extended descriptions would show, amply enforce the generic distinction of Xyris within the family.