Foliar sclereids and vein sheaths in the New Caledonian species of Scaevola L. (Goodeniaceae)

Iris H. Müller
1989
Müller I. H. 1989. Foliar sclereids and vein sheaths in the New Caledonian species of Scaevola L. (Goodeniaceae). Bot. Helv. 99: 65-72. The leaf sclereids and veinlet sheaths of 9 species of Scaevola are described and illustrated. Individual sheath cells and sclereids showed some Variation in lignification and shape. The structure of the leaf sclereids and veinlet sheaths is characteristic for the species. A key based on vegetative characters is given. Key Key to the New Caledonian species of
more » ... aevola, based on anatomical characters. 1A. veinlets devoid of sheathing; sclereids angular, not exceeding 100 Lim S. taccada 1 B. veinlets with prominent sheathing 2A. wall of sclereids as thick as lumen (fig. 5) 3 A. outer surface of sheath cells with papilla-like Protrusion, sclereids 8B. density of sclereids per 1/2 mm2: 8-16, number of elongated bündle sheath cells near vein endings: (0)-1 -5 S. montana* Discussion The present study shows that characters of sclereids and vein sheaths are often important for distinguishing species. Rao (1980) stressed that examination in many taxa showed the sclereids to be an important diagnostic tool for future revisionary studies. The function of sclereids is not yet fully understood, and in spite of widely divergent explanations, as, e.g., a mechanical function, or constituting a dump for noxious substances. However, their usefulness in taxonomy has been shown many times. In the species examined, two types of sclereids (sensu Rao & Bhupal 1973 , Rao 1980 ) can be distinguished: monomorphic and cacomorphic In S. beckii, S. coccinea, S. racemigera and S. taccada sclereids of the first type occur, whereas the remaining species possess sclereids ofthe second type. Although phylogenetic conclusions based on the distribution of sclereids do not seem to be feasible as yet (Thorne 1983), it appears that in some cases, sclereid features may provide supporting evidence for taxonomie grouping (Rao & Nayak , Foster 1946)) . * These species pair gives some difficulties in the differentiation, the characteristics used cannot separate them clearly.
doi:10.5169/seals-69130 fatcat:lm356r464vegtmmf6zeqnrfnmm