Development of ovule, fruit and seed of X yris ( X yridaceae, P oales) and taxonomic considerations

The development of the ovule, fruit and seed of X yris spp. was studied to assess the embryological characteristics of potential taxonomic usefulness. All of the studied species have (1) orthotropous, bitegmic and tenuinucellate ovules, with a micropyle formed by both the endostoma and exostoma; (2) a cuticle in the ovules and seeds between the nucellus/endosperm and the inner integument and between the inner and outer integuments; (3) helobial, starchy endosperm; (4) a reduced, campanulate and undifferentiated embryo; (5) a seed coat formed by a tanniferous endotegmen, endotesta with thick‐walled cells and exotesta with thin‐walled cells; and (6) a micropylar operculum formed from inner and outer integuments. The pericarp is composed of a mesocarp with cells containing starch grains and an endocarp and exocarp formed by cells with U ‐shaped thickened walls. The studied species differ in the embryo sac development, which can be of the P olygonum or A llium type, and in the pericarp, which can have larger cells in either endocarp or exocarp. The A llium ‐type embryo sac development was observed only in X yris spp. within X yridaceae. X yris also differs from the other genera of X yridaceae by the presence of orthotropous ovules and a seed coat formed by endotegmen, endotesta and exotesta, in agreement with the division of the family into X yridoideae and A bolbodoideae. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society , 2015, 177 , 619–628.