Anatomy and germination of diaspores of Chrysolaena cognata (Less.) Dematt. (Asteraceae)

Abstract

Despite the wide distribution of Chrysolaena cognata (Less.) Dematt. (Asteraceae) in south-central Brazil, there are no data in the literature on germination or on the structure of its diaspores. Thus, inflorescences with flowers and diaspores in development were fixed in FAA solution, sectioned at 9-11?m and analyzed in light microscopy. For germination analysis, the diaspores were kept in a germination chamber under different temperatures and were subsequently evaluated for germination percentage, germination speed index, and mean germination time. Glandular trichomes exist in the ovary and twin hairs occur in the external epidermis, both remaining in the mature fruit. In the part of the developing seed, the mesophyll and inner epidermis of the ovule are collapsed. The ripe fruit is devoid of phytomelanin, the pappus is persistent and the outer mesocarp is sclerenchymatous. In ripe seeds, the integument is unspecialized and the embryo is straight. In relation to germination, the diaspores presented higher IVG and lower average germination times when kept under a temperature of 20 °C. The results obtained demonstrate that C. cognata follows the typical pattern of Asteraceae cypsela (achene), and the germination performance depends on the environmental conditions of the growth location.

Keywords: cypsela, ovary, pericarp, temperature.