Research observations: Standardized terminology for structures resulting in emergence and crown placement of 3 perennial grasses

Abstract

A significant problem we encountered in grass establishment research was confusion in the literature over seedling structures and terminology. From review of the historical literature and our observations of growth-chamber grown sideoats grama [Bouteloua curtipendula (Michx.) Torr.] western wheatgrass [Agropyron smithii Rydb.; new cytogenetic = Pascopyron smithii Rydb. (Loeve)l and smooth bromegrass (Bromus inermis Leyss.) seedlings, we suggest standard structures and terminology for grass seedlings. The nodes of a grass seedling are defined as the scutellar node, coleoptilar node, and leaf nodes named in sequence from first to last. The internode between the scutellar and coleoptilar nodes is termed the mesocotyl. The internode that develops inside the coleoptile between the coleoptilar and first leaf nodes is defined as the first leaf internode. Subsequent internodes are named for the leaf node immediately above; e.g., second leaf internode. Using these structures and terminology we found the "mechanism" of emergence for these grass seedlings from a 25-mm seeding depth was elongation of the mesocotyl (when expressed) and elongation of the coleoptile. Sideoats grama had a long mesocotyl and short coleoptile; western wheatgrass lacked or had a short mesocotyl and a long coleoptile; and smooth bromegrass had intermediate mesocotyl and coleoptile lengths. The "mechanism" of crown placement for seedlings that emerged and survived from a 51-mm seeding depth was non-elongation or elongation of the mesocotyl and leaf internodes. The crowns of sideoats grams seedlings were at the coleoptilar node, which was close to the soil surface. Western wheatgrass seedlings have their crowns near planting depth, usually at the coleoptilar node. Smooth bromegrass crowns were at variable depths because of variable elongation of the mesocotyl and leaf internodes.