Anatomical wood variation of Buddleja cordata (Buddlejaceae) along its natural range in Mexico

Buddleja cordata is an evergreen species of wide distribution in Mexico that is represented by shrubs and trees. Wood variability of B. cordata was evaluated in relation to plant size as well as latitude, altitude, soils, and climatic data. Canonical correlation analysis (CCA) showed that two canonical correlations are significant (Wilks' lambda, p < 0.0001) and explained 76% of total variance. Redundancy analysis revealed that the first pair of canonical variates are significant, thus the canonical variate, named distribution, represents a gradient of maximum temperature of the warmest period, annual temperature range, and latitude in its area of distribution; whereas the canonical variate named wood represents vessel density, fiber length, and plant size, best associated to the environmental gradient. Vessel density expressed by its distribution in latewood and porosity type showed that ring-porosity is common in individuals from high latitudes. Temperatures below zero or lack of rainfall during several months might induce porosity variability in B. cordata as suggested by CCA, but was not related to phenology since the species is evergreen along its latitudinal range. Plant size was also influenced by extreme temperature and rainfall. Shorter plants are distributed in the northern population or driest sites located in north-central Mexico, and in addition, fiber length followed an allometric relation with individuals' height. Wood characters in B. cordata as for simple perforation plate, helical thickenings, type of intervascular and vessel-ray pits, scanty paratracheal parenchyma, and heterogeneous type IIB rays were not correlated with plant size, climate, and soil parameters or species distribution. These features are common with other species of Buddleja.