Six Hakea species varying greatly in seed size were selected for cotyledon damage experiments. The

growth of seedlings with cotyledons partially or completely removed was monitored over 90 days. All

seedlings perished by the fifth week when both cotyledons were removed irrespective of seed size.

Partial removal of cotyledons caused a significant delay in the emergence of the first leaf, and reduction

in root and shoot growth of the large-seeded species. The growth of seedlings of small-seeded species

was less impacted by cotyledon damage. The rate of survival, root and shoot lengths and dry biomass

of the seedlings were determined after 90 days. When seedlings were treated with balanced nutrient

solutions following removal of the cotyledons, survival was 95–98%, but 0% when supplied with

nutrient solutions lacking N or P or with water only. The addition of a balanced nutrient solution failed

to restore complete growth of any species, but the rate of root elongation for the small-seeded species

was maintained. Cotyledons provide nutrients to support early growth of Hakea seedlings, but other

physiological roles for the cotyledons are also implicated. In conclusion, small-seeded Hakea species can

tolerate cotyledons loss better than large-seeded species.

Seed size is a key functional trait that affects plant fitness at the seedling stage and may

vary greatly with species fruit size, growth form and fecundity. Using structural equation

modelling (SEM) and correlated trait evolution analysis, we investigated the interaction network

between seed size and fecundity, postfire regeneration strategy, fruit size, plant height

and serotiny (on-plant seed storage) among 82 species of the woody shrub genus, Hakea,

with a wide spectrum of seed sizes (2–500 mg). Seed size is negatively correlated with fecundity,

while fire-killed species (nonsprouters) produce more seeds than resprouters

though they are of similar size. Seed size is unrelated to plant height and level of serotiny

while it scales allometrically with fruit size. A strong phylogenetic signal in seed size revealed

phylogenetic constraints on seed size variation in Hakea. Our analyses suggest a

causal relationship between seed size, fecundity and postfire regeneration strategy in

Hakea. These results demonstrate that fruit size, fecundity and evolutionary history have

had most control over seed size variation among Hakea species.

تمت إضافة ثلاثة أنواع نباتية للفلورا الليبية هي Ruta montana + Pimpinella cretica + plantago bellardii

تمت إضافة ثلاثة أنواع نباتية للفلورا الليبية هي Lactuca saligna + Sanguisorba minor