Variation among 91 stone oak species (Fagaceae, Lithocarpus) in fruit and vegetative morphology in relation to climatic factors

Abstract

Stone oaks (genus Lithocarpus, Fagaceae) are common canopy trees in the tropical and subtropical forests across China and Southeast Asia, which exhibit both great species diversity and interspecific variation in fruit morphology represented by two major fruit types. Acorn (AC) fruits of Lithocarpus are similar to oak (Quercus) acorns, and enclosed receptacle (ER) fruits generally have larger seeds enclosed by thick lignified fruit husks. It is therefore worth examining the adaptation of stone oaks to a wide range of ecosystems and climatic conditions by interspecific functional differentiation for understanding their diversification. By applying the herbarium-specimen database (20,516 specimens) and records from the Flora of China, we examined the variation in both reproductive (seed, fruit husk and cupule size) and vegetative (leaf length, leaf width and maximum tree height) traits among 91 species, in relation to climatic factors (mean annual temperature and wetness annual precipitation minus annual potential evapotranspiration). We found that even though species representing both fruit types co-occurred over Southern China, they exhibited different correlations with climatic factors: three reproductive components of AC fruits were all positively related to both temperature and wetness, whereas only husk volume of ER fruits representing mechanical protection to seed increased with temperature. In vegetative traits, leaf length and tree height of ER-type species were both negatively related with excessive wetness. Our results suggested that vegetative traits of stone oaks were independent of fruit types and fruit morphological variations. Overall, the distinctive correlation between interspecific reproductive and vegetative traits with climatic factors could be important in the diversification of the stone oaks in the tropical and subtropical evergreen broad-leaved forests.