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

Corresponding with the equitant habit of leaves, Achlyphila disticha shows anatomical features unusual or unique in Xyridaccne. Among these features are the sclerified epidermis, the bands of sclerenchyma in the leaf sheath, and the central zone of thick-walled parenchyma in the upper portions of the leaf. A transeetion of the sheathing portion of the leaf (fig. 45) shows three distinct zones of mesophyll: the outermost consists of spherical chlorenchyma cells; interior to this is a band of sclerenchyma in which the bundles lie. This sclerenchyma zone represents the widening, and fusion, of the individual selerenchymatous bundle sheaths, which are separate at higher levels (figs. 46, 47) in the leaf. The innermost layers, present only on the adaxial surface of the central leaf sheath (fig. 46), consist of thick-walled parenchyma cells, isodiametric and polygonal in transeetion. Because of the equitant habit, sections at higher levels show the fusion of the two halves (fig. 46) into a conformation elliptical in transeetion (fig. 46). Here the bundles and their sheaths are separate, with no intervening sclerenchyma. The chlorenchyma can be differentiated into palisade and spongy at this level. The cells at the dorsal and ventral edges of the leaf (sclerified epidermis) are prominently elongate as seen in transeetion, forming irregular shapes. As seen in longitudinal section (fig. 39), the adjacent edges of epidermal calls are often raised into emergences, whereas the central surface of such cells is depressed. This configuration of epidermal cells is reported by Solereder and Meyer (1929) for several Xyris species and figured for X. montivaga. The elongate sclerified epidermal cells, as seen in transeetion, closely match those which Arber (1925) figures for X. anceps, although this species, unlike X. montivaga, does not have the undulate contours of epidermal cells as seen in longitudinal section. Sections of the leaf of Achlyphila at the level shown in figure 47 show that the central parenchyma of the leaf is thickwalled, probably lignified, and has an elliptical shape. At higher levels, there is a diminution both in the area of the central parenchyma and the number of bundles which surround it.

Discussion.

Malme's claim in 1925 that leaf anatomy is rather stereotyped in Abolboda as compared to Xyris, except for the number of veins, does not appear to be justified on the basis of the present study. A number of seemingly excellent specific and species-group characteristics have been described above. Leaf anatomy of Orectanthe reveals the similarity of that genus to Aboiloda as well as the generic distinctions of the two species.

The leaf of Achlyphila is not unlike those of other Xyridaceae in its general structure. For example, Xyris asperaia has a similar equitant habit (although the anatomy is quite different), as illustrated by Arber (1925). The presence of a ring of bundles around a zone of thick-walled parenchyma seems unique in the family, however. The epidermal characteristics although quite unlike those of Abolboda and Orectanthe, find parallels in Xyris.

Vessels.

Although Solereder and Meyer (1929) do not mention the occurrence of vessel elements in leaves of Xyridaceac, longitudinal sections of leaves revealed vessel elements with simple perforation plates in the following species: Abolboda lincarifolia, A. macrostachya var. angustior, A. macrostachya var. macrostachya, and A. macrostachya var. robustior. Vessels, therefore, definitely do occur in leaves of at least the larger-leaved species of Abolboda. Vessels with simple perforation plates are indicated by Cheadle (1942) for leaves of Xyris flexuosa and X. stuailiana.