Evolution ecology and structure of secondary xylem of mangroves

A study on the relation between the evolution and structure of secondary xylem of the mangrove Bruguiera sexangula,B.uguiera gymnerrhixa,Ceriops tagal and Kandelia candel (Rhizophoraceae).Avicennia marina (Verbenaceae),Aegiceras eorniculatum (Mysinaceae) and Sonneratia caeseolaria (Sonneratiaceae) is made.The results are shown as follows:Secondary xylem of mangrove species in Rhizophoraceae is more primitive than those of mangrove species in Verbenaceae,Mysinaceae and Sonneratiaceae,Carallia and Pellacalyx belong to Rhizophoraceae of terrestrial plants but are not mangrove species and they have more evolutionary secondary xylem,namely,simple perforation vessel and alternate pit-pair,than mangrove species such as Bruguiera,Ceriops and Kandelia (Rhizophoraceae).The form of simple perforation vessel is a specialization phenomenon in dry environment during the long evolution.But the secondary xylem characteristics of mangrove species in Rhizophoraceae remained primitive,after they entered the seashore wetlands.