Seed morphology and seed coat micromorphology of Linaria cretacea Fisch. ex Spreng. from chalk outcrops of Western Kazakhstan

Abstract

The investigation of seed morphology and seed-coat micromorphology is important for taxonomy, ecology, and the conservation of rare endemic plants, particularly species restricted to specialized habitats such as chalk outcrops. In calciphilous plants with narrow distribution ranges, seed-coat micromorphology can serve as a useful diagnostic feature for species identification, clarification of taxonomic relationships, and the development of ex situ conservation measures. This study examined the morphological characteristics of the seeds and fruits of Linaria cretacea Fisch. ex Spreng., a rare calciphilous endemic species restricted to chalk outcrops in Western Kazakhstan, using scanning electron microscopy (SEM) and light microscopy. Macro- and microimages of the seeds were obtained, and their main morphometric parameters, including length, width, thickness, and shape index, were measured. Seed-coat sculpture was described at the primary, secondary, and tertiary levels following the classifications proposed by W. Barthlott and W. Stearn. The results showed that L. cretacea from the Aktobe Region is characterized by a cerebelliform primary sculpture with clearly defined anticlinal boundaries, a sharply tuberculate secondary sculpture with reticulate elements, and the absence of epicuticular wax. Comparison of the seed-coat traits identified in this study with published descriptions of the closely related species L. vulgaris and L. genistifolia revealed a set of diagnostically significant micromorphological differences. The possible adaptive role of seed-coat structure in chalk habitats with low water-retention capacity is also discussed. The findings are of both systematic and practical value, particularly for the identification of herbarium specimens and the development of protection and ex situ conservation protocols for this rare species..