EVOLUTION OF SPORE MORPHOLOGY IN THE BLECHNACEAE

Premise of research. In the recent past, nine to 12 genera of Blechnaceae have been generally recognized. Nowadays, 24 are accepted on the basis of recent molecular phylogenetic studies, and these genera are classified into three subfamilies. The purpose of this article is to optimize spore characteristics of the exine and perine on a phylogenetic tree, infer their evolution within the Blechnaceae, and determine whether the characters define any of the genera or subfamilies. Methodology. With an SEM, we imaged spores of four outgroup species and 88 species of Blechnaceae. On the basis of the images, we recognized and scored four characters: perine overall architecture (three states), perine microstructure (10 states), number of perine layers (three states), and exine surface (three states). Using maximum parsimony, we optimized these characters on a phylogenetic tree created from accessions in GenBank for the species we imaged. Pivotal results. Ancestral for the Blechnaceae is a smooth exine, three-layered perine, loose perine structure (i.e., the perine is not adnate to the exine), and the presence of broadly rounded perine folds. The exine evolved from the smooth (ancestral) state to low verrucate in Lomariocycas and from smooth to contoured (with tubercles or short ridges aligned nearly parallel to each other) in subfam. Stenochlaenoideae. Also in subfam. Stenochlaenoideae, the perine was reduced to only one layer, and spherical deposits were present on the outer surface of the perine. These spherical deposits were found in no other genus in the family. A contoured exine also evolved in Diploblechnum. Parablechnum has the unique perine character of tortuous filaments. The perine of Lomaridium is distinctive by the combination of narrow folds creating wide intramural areas and the presence of granulate deposits. Sadleria was the only genus in the family that has a fibrillose or foliaceous perine. The spores of Austroblechnum were distinctive by a nonfolded perine that was smooth or with granulate deposits. Throughout the Blechnaceae, when the middle layer of the perine is present, it contains many small lacunae imparting a spongy appearance, thus distinguishing the layer from the inner and outer layers. Conclusions. Characters of the exine and perine vary within the Blechnaceae and are useful in defining clades within the family. The most distinctive spores belong to subfam. Stenochlaenoideae, which have a tuberculate or short-ridged exine, a perine reduced to a single thin layer appressed to the exine, and the presence of spherical deposits. Many genera of Blechnaceae are characterized by a combination of perine characters.