terms to know for grass anatomy
One of the
To become proficient at identifying grasses, you must be able to recognize a spikelet. A grass spikelet is normally made up of a pair of glumes enfolding one or more florets, which contain the grass flowers. Spikelets come in a variety of shapes and sizes. Sometimes there is only one glume and occasionally glumes are missing entirely. The florets are normally made up of a lemma and a palea enfolding the male and female parts. Spikelets can be round (cylindrical), laterally compressed (flattened), or dorsi-ventrally compressed.
This is a spikelet of Deschampsia: two florets with lemmas awned from the back are contained within two glumes that are longer than the florets; the rachilla (stalk between the florets) is hairy.
This is a spikelet of a needle or ricegrass (Achnatherum): the two glumes enclose a single floret that is awned from the tip of the lemma.
This is a spikelet of lovegrass (Eragrostis): two glumes subtend numerous florets. None of the lemmas are awned; they have glands instead.
This is a spikelet of ryegrass (Lolium): one side of the spikelet has a glume and the other side is tucked into the rachis (which serves as a substitute for a second glume). The topmost spikelet in each spike has two glumes.
The spikelet of rabbitsfoot grass (Polypogon) has only one floret, and the glumes have long curving awns.
The spikelets of quaking grass (Briza) have several unawned florets and dangle from panicle branches.
Dorsi-ventrally compressed spikelets are flattened from front to back. The "back" is where the central vein is located. Think of your spine as being the central vein and that your body is wider from side to side than front to back. That's dorsi-ventrally compressed. In contrast, the shape of a trout is laterally compressed. Examples of genera with dorsi-ventrally compressed spikelets are Panicum, Paspalum, Echinochloa, and Digitaria.
A spikelet of bristlegrass (Setaria) showing the cluster of bristles below it. In this side view, you can see both the lower and upper glumes and the lower and upper lemmas. The lower lemma is sterile and has no palea. The upper lemma is fertile and is the one with the wrinkles on its surface.
This is the spikelet of Paspalum dilatatum, dallisgrass. The image on the left shows the upper glume and lower lemma, which have a fringe of long hairs. There is no lower glume. In the image on the right the upper glume has been removed to show the upper (fertile) floret. The purple plumes are the stigmas, the female flower part that catches airborne pollen.