Monographs Details: Orectanthe
Authority: Carlquist, Sherwin. 1960. Anatomy of Guayana Xyridaceae: Abutboda, Orectanthe and Achtyplola. Mem. New York Bot. Gard. 10: 63-117.
Family:Xyridaceae
Scientific Name:Orectanthe Maguire
Discussion:

No roots of Orectanthe were available for study.

Vessels.

For each of the above species, serial longitudinal sections were prepared to show the presence of vessels. All the species described above proved to have true vessel elements with simple perforation plates. Vessels have been reported by Solereder and Meyer (1929) in roots of Xyris laccra, X. lannia, and A", indica. Likewise, Cheadle (1942) indicates vessels with simple perforation plates for roots of Xyris fl.rxnosa and A'. smalliana.

Discussion.

The species of Abolboda described here offer no features not previously mentioned by Solereder and Meyer for Abolboda, or Xyris. The possibility that endodermis-cell characteristics could be used as specific characteristics, suggested by Malme in 1925, appears to be valid. Malme shows very thick-walled endodermal cells with centrally placed lumina for A. pulchella and A. vaginata. He reports prominent thickenings on the inner wall, tapering sharply on the radial walls, and absent on the outer walls, for endodermal cells in roots of A. poeppigii, A. grandis, and A. macrostachyo. Malme's figure for A. macrostachya is markedly different from the condition illustrated here for that species. The endodermal cell thickenings Malme reports for A. poarchon and A. abbreviata are like those illustrated in the present study for A. aeieularis.

Interestingly, Malme's figures all show an uninterrupted perieycle (A. vaginata, A. macrostachya, A. poarchon). The species of Abolboda in the present study in which uninterrupted perieycle was observed all belong to the group termed "larger-stemmed abolbodas" in sections below. Malme's figures also suggest a larger number (six or more) of xylem poles, a feature also characteristic of the group just named. Thus as Malme (1925) claims, different types of root anatomy in Abolboda appear to be characteristic of species or speciesgroups; from the example of A. sprue ci described above, one may surmise that such characters are not always limited to the stele, but may be found in the cortical zone as well.

The several layers of cells between endodermis and outermost vessels, the absence of central vessels, the presence of endodermis-like cells in their place, and the distinctively staining endodermis thickenings are characteristics which, taken together, would seem to give the roots of Achlyphila a generic differentiation from the other three genera. In fact, some of these characteristics seem new to Xijridaceae, althoug-h the sum of characteristics in this genus would not exclude it from the family.

On the basis of the present study, one may conclude that the roots of Abolboda offer no anatomical features (other than greater size, and therefore more numerous vessels) which cannot also be found in Xyris roots, as the account of Solereder and Meyer (1929) illustrates.

STEM

As the summary of Solereder and Meyer shows, remarkably little is known about stem anatomy in Xyridaceae. The only facts that have been established are that bundles are amphivasal, individual bundles may be sheathed with sclerenchyma (incompletely in A". Janata), and that (in X. lanata) the bundles may form concentric bands. As an additional generalization, the writer would like to add the fact that in all taxa he examined, vascular bundles tend to be more or less amphivasal except where they are demarcated as leaf traces, in which case the structure of the bundles tends to be more nearly collateral.

The data given below are derived from study of mature portions of rosette stems, except for Achlyphila, which has a rhizomatous habit. At and near the base of a stem, especially in the smaller-stemmed species of Abolboda, departing roots may be numerous in the cortex, and the vascular bundles may form a very small group in the center of the stem. In A. americana, no part of the stem (except the very youngest) was free from departing roots. The types of stem anatomy observed in the Xijridaceae under study here fall into four main groups.