Variation in the organization of the stomatal complex in the leaf epidermis of monocotyledons and its bearing on their phylogeny

Abstract

Using macerated pieces of epidermal tissue from living plants and herbarium specimens, stomatal complexes of 192 species belonging to 49 families of monocotyledons were studied. Four categories are recognized, 2 with 4 or more subsidiary cells surrounding the guard cells, 1 with 2 subsidiaries, and 1 with none. Development of the 2-subsidiary type, studied in acetocarmine preparations of Juncus effusus and Sagittaria montevidensis, resembles that in Gramineae previously described. No correlation was found between type of stomatal complex and either leaf shape or type of xylem vessel, but some correlation exists between this character and type of seed germination, vascular anatomy of seedling, growth habit of mature plant, and geographic distribution. Types with 4 or more subsidiaries are most commonly phanero phytes with tropical distribution, many vascular bundles in the cotyledon, and hypogeal germination. Complexes with 2 subsidiaries occur in many families of a diverse nature, but the most primitive plants with this type are hydrophytes or helophytes with tropical or temperate distribution, 1 vascular bundle in the cotyledon, and epigeal germination. Stomatal complexes without subsidiaries are almost confined to the Liliales and their more specialized derivatives. These plants are predominantly geophytes with temperate or tropical distribution, 2 bundles in the cotyledon, and epigeal germination. Reasons are advanced for suggesting that the type with many subsidiaries is the most primitive and the other 2 types have been derived from it independently by reduction of the number of subsidiary cells.