PATTERNS OF CUTICULAR SCULPTURE IN THE HYBRID, CUPRESSOCYPARIS LEYLANDII (JACKSON AND DALLIMORE) DALLIMORE, AND ITS PUTATIVE PARENTS

Abstract

The circumstances of the origin of X Cupressocyparis leylandii (Jackson and Dallimore) Dallimore, its subsequent propagation and comparison of morphology with its putative parents Chamaecyparis nootkatensis (D. Don) Spach and Cupressus macrocarpa Hartw., have been described by Ovens, Blight and Mitchell (1964), van de Laar (1968) and Mitchell (1972). Although its hybrid status has not yet been proved by breeding and other genetic experiments, the problem might be approached via genotypic variability of cuticular features. Increasing use has been made of cuticular characters in various taxonomic studies (e.g. Stace, 1965, Stockey and Taylor, 1978; Miranda and Chaphekar, 1980). The present study attempts to compare the leaf cuticles of X Cupressocyparis leylandii and its putative parents. The cuticles were macerated in 20 0 chromium trioxide for 16 h at room temperature for subsequent examination by scanning electron microscopy (Alvin and Boulter, 1974; Oladele, 1982). Integrity of the cuticle was not affected, although the extracuticular wax may be partly dissolved by the treatment, particularly for periods longer than 16 h. Examination of the inner surface of the cuticles isolated from the abaxial surface of the leaves, reveals sculpture patterns consisting essentially of two main features the macrorelief formed by the anticlinal or radial flanges and the microrelief of the periclinal or tangential surface (Fig. 1). The hybrid shows intermediacy in two features of the radial flanges, namely continuity of the flange and the radial flange buttress. The radial flange is sparsely interrupted in Cupressus macrocarpa [Fig. 1 (c)], highly interrupted in Charnaecyparis nootkatensis [Fig. 1 (a)] and less so in X Cupressocyparis leylandii [Fig. 1 (b)]. Along the base of radial flange is a swelling which resembles a buttress to the flange; this is absent in Cupressus macrocarpa [Fig. 1(c)], very prominent in Chamaecyparis nootkatensis [Fig. 1(a)] and intermediate in the hybrid [Fig. 1(b)]. However, the microrelief or surface sculpture of the tangential surface and of the radial surface do not show intermediacy in the hybrid. The sculpture is complex in Chamaecyparis nootkatensis, in which coarse granules predominate, with other less prominent and fewer granules. The cavities also form a complex branching pattern among the granules [Fig. 1 (d)]. In Cupressus macrocarpa, surface granulation is rather more uniform, with greater density of small elements [Fig. 1(f)]. The surface in the hybrid is comparatively smooth with only small, rather uniform widely spaced granules [Plate 1(e)]. Nor do the granules in the hybrid show intermediacy in size as they are smaller (04 4tm in diameter) than those of