1960] 



ANATOMY OF GUAYAXA XYRIDACEAE 



85 



Achlyphila. 



• Corresponding with the equitant habit of leaves, Achlyphila disticha shows 

 anatomical features unusual or unique in Xyridaceae. Among these features 

 are the sclerified epidermis, the bands of sclerenehyma in the leaf sheath, and 

 the central zone of thick-walled parenchyma in the upper portions of the leaf. 

 A transection 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 sclerenehyma in which the bundles lie. This scleren- 

 ehyma zone represents the widening, and fusion, of the individual sclerenchyma- 

 tous 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, isocliametric and 

 polygonal in transection. Because of the equitant habit, sections at higher 

 levels show the fusion of the two halves (fig. 46) into a conformation elliptical 

 in transection (fig. 46). Here the bundles and their sheaths are separate, with 

 no intervening sclerenehyma. 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 transection, 

 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 re- 

 ported by Solereder and Meyer (1929) for several Xyris species and figured 

 for X. montivaga. The elongate sclerified epidermal cells, as seen in transection, 

 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 thick- 

 walled, 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 Abolboda 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. 



portions of the two wings. X 70. Fig. 47. Transection of upper (equitant) portion of leaf, 

 showing slightly more than half; orientation as in figure 46 — morphologically adaxial por- 

 tion of leaf above. X 80. 



