Summary of Grass Morphology and Species Identification

## Introduction *Cynodon* is a genus of grasses known for species used in lawns, forages, and erosion control. In this material, we focus on comparative morphological descriptions of three species: **Cynodon nlemfuensis**, **Cynodon plectostachyus**, and **Cynodon dactylon**, and on how to recognize their inflorescences, spikelets, glumes, and florets. This content helps university students identify and compare diagnostic characteristics useful in the field and herbaria. > Definition: *Cynodon* is a genus of perennial grasses with creeping or caespitose stems, inflorescences in spikelet racemes, and common use as turf and forage. ## General Inflorescence Structure ### Main Components - **Raceme**: the inflorescence unit in Cynodon; each plant features several racemes arranged in a compound inflorescence. - **Rachis**: the axis of the raceme; in these species, it is typically flattened. - **Spikelets**: small floral units which are arranged laterally (broadside) to the rachis, forming a double row (2-rowed). > Definition: A raceme is a type of inflorescence in which flowers (or spikelets) are attached by unequal pedicels along a central axis. ### Common Characteristics Described - Racemes: generally unilateral (all spikelets oriented to one side) and numbering 3–7 or 4–6 depending on the species; typical length $1.5$–$8$ cm. - Rachis: flattened, with spikelets packed broadside to the rachis (2-rowed). - Spikelets: often appressed (pressed tightly against the rachis) and fertile ones are sessile (without a pedicel). ## Comparison of the Three Species (Summary Table) | Attribute | Cynodon plectostachyus (African Star Grass) | Cynodon nlemfuensis (St. Domingo Star Grass) | Cynodon dactylon (Bermudagrass) | |---|---:|---:|---:| | Inflorescence (racemes) | 4–6; unilateral; $1.5$–$6(–8)$ cm | 3–7 cm long; unilateral | 3–7 cm long; unilateral | | Rachis | Flattened | Flattened | Flattened | | Spikelet Arrangement | Broadside to rachis; 2-rowed | Broadside to rachis; 2-rowed | Broadside to rachis; 2-rowed | | Fertile Spikelets | Sessile; appressed; 1 fertile floret; ovate; $2.5$–$3$ mm | Sessile; appressed; 1 fertile floret; ovate; $2$–$3$ mm | Sessile; appressed; 1 fertile floret; ovate; $2$–$2.5$ mm | | Disarticulation | Disarticulates below each fertile floret | Disarticulates below each fertile floret | Disarticulates below each fertile floret | | Glumes (lower / upper) | Lower ovate $0.2$–$0.3$ mm; upper ovate $0.4$–$0.6$ mm; persistent; subequal in width | Lower lanceolate; as long as the upper; upper lanceolate $0.5$–$0.8$ length of the fertile lemma; persistent | Lower lanceolate; as long as the upper; upper lanceolate $0.5$–$0.8$ length of the fertile lemma; persistent | | Fertile Lemma | Ovate; laterally compressed; $2.5$–$3$ mm; cartilaginous; 3-veined; midvein ciliate | Ovate; laterally compressed; $2$–$3$ mm; cartilaginous; 3-veined; midvein pubescent or ciliate | Ovate; laterally compressed; $2$–$2.5$ mm; cartilaginous; 3-veined; midvein pubescent | | Palea | 2-veined; keels ciliate in C. plectostachyus; eciliate in C. dactylon | 2-veined | 2-veined | | Fruit | Caryopsis with adherent pericarp | Caryopsis with adherent pericarp | Caryopsis with adherent pericarp | > Definition: A lemma is the outer bract of a floret in grasses, often protecting the flower and seed. ## Useful Morphological Details for Identification ### Spikelets and Disarticulation - The three species have **spikelets containing a single fertile floret** and **disarticulate below the floret** upon maturity; this facilitates the dispersal of the caryopses. ### Glumes - Glumes are **persistent**, thinner than the fertile lemma, and **lack visible lateral veins** in the described species. Their shape and relative size (lanceolate vs. ovate; proportion to the lemma) help distinguish *C. plectostachyus* from the others. ### Lemma and Palea - Lemmas: all are ovate, cartilaginous, and have 3 main veins; variations in length ($2$–$3$ mm) and the type of