back

GRASS SPIKELET FORMULA

The grass spikelet formula as used here summarizes some of the important data for grass identification. The ideas are expanded from those discussed in The grass spikelet formula: an aid to teaching and identification by K.W. Allred and J. T. Columbus [J. of Range Mgmt. 41(4): 350-351]. The spikelet formula somewhat follows the long used notations for floral formulas used for all flowering plants in books like Plant Systematics by S. B. Jones and A. E. Luchsinger [McGraw-Hill, Inc., 1986] and Vascular Plant Taxonomy by D. R. Walters and D. J. Keil [Kendall/Hunt Publishing Company, 1996].

Each spikelet formula represents information for each of the 142 genera of Texas Grasses. Information is summarized about glumes (G), fertile florets (F), reduced florets (R), spikelet disarticulation (a line above or below glumes), and inflorescence type(s). The parts are placed in the same sequence as the spikelet they represent.

Example:

Additional information can be summarized in the formula by adding superscripts and subscripts to the left and right of the R, F, and G. The superscript to the left indicates the number of awn per lemma, superscript to the right indicates the number of parts (e.g. G 2 = glumes two); subscripts to the right indicate the number of veins (e.g. F 3= fertile floret lemma 3-veined). Other important features of the spikelet(s) and inflorescence(s) for grass genera that typically have unisexal spikelets are represented by a formula for both the pistillate and staminate spikelets.

= glumes absent
= one glume present (usually the second)
= spikelet disarticulation below the glumes
= spikelet disarticulation below glumes, glumes two, 1-awned
= fertile floret 1
= fertile floret(s) 1 (occasionally 2)
= fertile florets 2-several
= fertile florets 3-5 veined
= fertile floret lemma awnless
= Fertile floret lemma 1-awned
= reduced floret absent (occasionally 1)
= reduced floret lemma 1-awned
= reduced floret lemma 3-veined
pan = panicle inflorescence
spicate raceme = spicate raceme inflorescence
raceme = raceme inflorescence
spike = spike inflorescence
pan spic 1o unil br = panicle of spicate primary unlateral branches

Examples of spikelet formulae representing several genera are listed below:

Bromus
Panicum
Paspalum
Schizachyrium
Chasmanthium
Leersia
Distichlis