Kellogg Elizabeth A
Harvard University Herbaria, 22 Divinity Avenue, Cambridge, MA, 02138, USA.
Evolution. 1990 Dec;44(8):1978-1989. doi: 10.1111/j.1558-5646.1990.tb04304.x.
Species distinctions in grasses are based on differences in sizes of parts, particularly floral parts, and on differences in distribution of hairs; both sets of characters are apparently subject to repeated parallel evolution. Developmental studies of florets in the genus Poa reveal that there are only two developmental trajectories for lemma length relative to anther length (a measure of time to maturity): either lemma growth is continuous with anther growth, or the lemma reaches its adult size well before the anthers do. The tuft of long, cobweb-like hairs on the callus of many species forms early in lemma development, as might be expected for a character that marks a large group of species. The five possible patterns of hair distribution on the lemma itself represent stages of a single developmental pathway; differences between species presumably reflect differences in timing of onset or truncation of the developmental program (heterochrony).
禾本科植物的物种区分基于各部分大小的差异，尤其是花部的差异，以及毛的分布差异；这两组特征显然都经历了反复的平行进化。对早熟禾属小花的发育研究表明，相对于花药长度（衡量成熟时间的指标），外稃长度只有两种发育轨迹：要么外稃生长与花药生长连续，要么外稃在花药之前就达到其成年大小。许多物种稃基上的长而蛛丝状的毛簇在小穗发育早期形成，这对于一个标记一大类物种的特征来说是可以预期的。外稃上毛的分布的五种可能模式代表了单一发育途径的不同阶段；物种之间的差异可能反映了发育程序开始或截断时间的差异（发育异时性）。
