Intra-population variation in reproductive ecology and resource allocation of the rare biennial species Verbascum sinaiticum Benth., in Egypt

Verbascum sinaiticum Benth. (Scrophulariaceae) is a biennial rosette plant. The species is rare in Egypt and its distribution is restricted to the Sinai peninsula. The investigated population was located in Saint Catherine, Southern Sinai. To assess the reproductive ecology of the species the population dynamics, age-specific survival, resource allocation, energy content, and seed longevity of a natural population were studied. The germinable seed bank represents an average of 0•08% of the seeds in the seed rain. The plants are juvenile during 33% to 67% of their lives. Total seed rain output comes from four different cohorts of adult plants. Seeds produced during the summer constituted 83•5% of the total seed rain. Adult plants 15–18 months in age attained a maximum rosette leafiness of 2•85 m2m−2and a maximum root crown diameter of 2•3 cm. Highly reproductive individuals allocated the least dry mass to their roots. The root/shoot ratio was 0•25. Caloric content reached up to 6•37 kcal g−1dry mass in roots of juvenile plants and 7•5 kcal g−1dry mass in the summer seeds. Seed viability was higher in seeds produced during summer and autumn (9 years) as compared to seeds produced during spring (6 years). Life span ranges between 1 and 2 years, which results in an intra-population variation of survival, resource allocation, energy content, and seed longevity and viability. These variations act as an evolutionary filter, an important asset to increase the genetic diversity and stability of populations in areas with low or periodical rainfall.