Inflorescence Types
Grass inflorescences (Figures 1-3) are delimited by the uppermost culm leaf or portion thereof. By this definition, multiple inflorescences can occur on a single culm. We use the grass inflorescence terminology of spike, spicate raceme, raceme, and panicle in the traditional sense. Other terms are used for specialized panicle inflorescences. The spike, spicate raceme, and raceme inflorescences do not have branches arising from the central axis (rachis). With these inflorescences the spikelets either are attached directly or individually pedicelled (or stalked) upon the central axis. However, the panicle inflorescence has branches arising from the central axis nodes. The spikelets are seldom borne on the central axis, but on the branches. Spike inflorescences (Figure 1A) are those in which the spikelets are sessile on the central axis (rachis). A spicate raceme (Figures 1B and 3A) has an unbranched central axis (rachis) with sessile spikelets and short pedicellate spikelets at inflorescence nodes. Raceme inflorescences (Figure 1C) have pedicels supporting single spikelets, with the pedicel attached to the cental axis (rachis). Panicle inflorescences (Figures 1D, 2, and 3B-D) can have only primary branches or primary branches that branch and rebranch, or have several spikelets supported by each branch or branchlet. By definition, the central axis of a panicle is not a rachis. The rachis is only the axis of a spike, spicate raceme, or raceme.

A panicle of spicate primary unilateral branches (Figure 2) is a common modification of the typical panicle inflorescence. Branches developing from the nodes at the central axis of the inflorescence are called primary branches. Spikelets on this inflorescence type are racemose (subsessile) or spicate (sessile) on the primary branch and make the branch appear spikelike, hence the term "spicate." The spikelets are attached along one side of the branch and give the branch a unilateral or one-sided appearance. Panicles with spicate primary unilateral branches may be described by the arrangement of the branches using modifiers such as alternate (Figure 2A), digitate (Figure 2B), subdigitate (Figure 2C), or verticillate (Figure 2D).

A panicle of racemose branches (Figure 3B-D) is a specialized inflorescence composed of branches and branchlets bearing both sessile and pedicellate spikelets at each node; this condition, found in the Andropogoneae tribe, is repeated at all nodes of the inflorescence except the terminal node, where one sessile and two pedicellate spikelets are normal. The inflorescence types in the Andropogoneae tribe are spicate raceme (Figure 3A), panicle of subdigitate rames (Figure 3B), panicle of alternate rames (Figure 3C), and a panicle of rebranched rames (Figure 3D).

Figure 1. Diagrammatic representation and examples of grass inflorescence types: (A) spike (Lolium); (B) spicate raceme (Hordeum); (C) raceme (Bromus); and (D) open panicle (Dichanthelium). S=spikelet, CA=central axis, P=peduncle, SS=sessile spikelet, PS=pedicellate spikelet, and UL=uppermost leaf.

Figure 2. Diagrammatic representation and examples of grass inflorescence types: (A) panicle of alternate spicate primary unilateral branches (Bouteloua); (B) panicle of digitate spicate primary unilateral branches (Cynodon); (C) panicle of subdigitate spicate primary unilateral branches (Eleusine); and (D) panicle of verticillate spicate primary unilateral branches (Chloris). S=spikelet, CA=central axis, P=peduncle, and UL=uppermost leaf

Figure 3. Diagrammatic representation and examples of Andropogoneae tribe inflorescence types: (A) spicate raceme (Schizachyrium) ; (B) panicle of subdigitate rames (Andropogon); (C) panicle of alternate rames (Bothriochloa); and (D) panicle of rebranched rames (Sorghum). PS=pedicellate spikelet, CA=central axis, SS=sessile spikelet, and UL=uppermost leaf.