Understanding grass species morphology and identification is a critical skill for botanists, ecologists, and agricultural professionals alike. The intricate details of grass structures, from their overall habit to the minute features of their florets, provide the necessary clues for accurate identification. This article will delve into the distinct morphological characteristics of several important grass genera, including Bromus, Cynodon, Paspalum, Brachiaria, and Lolium, to help you master their identification.

Grass Species Morphology and Identification: An Overview

Grass plants exhibit a wide range of morphological features, which are systematically used for classification. These features include the habit (growth form), inflorescence structure, and the detailed characteristics of the fertile spikelets, glumes, and florets. By carefully observing these attributes, one can distinguish between closely related species.

Dissecting the Bromus Genus

The Bromus genus, commonly known as brome grasses, includes several species with distinct features. Let's examine Bromus carinatus, Bromus lanatipes, and Bromus catharticus.

Bromus carinatus: Key Identification Features

Habit: This is a short-lived perennial grass, typically growing 30–100 cm tall. Its leaf-sheaths are tubular, closed for 0.75 of their length, and pilose. Ligules are eciliate membranes (1–3 mm long), and leaf-blades are 3–12 mm wide.
Inflorescence: It forms an open, lanceolate panicle, 10–25 cm long, with appressed or ascending primary branches.
Fertile Spikelets: These are elliptic, strongly laterally compressed, 15–45 mm long, and contain 4–12 fertile florets. They disarticulate below each fertile floret at maturity.
Glumes: Glumes are persistent and dissimilar. The lower glume is lanceolate (5–9 mm long, 3-veined), and the upper glume is lanceolate (10–15 mm long, 5–7-veined), both with an acuminate apex.
Florets: The fertile lemma is ovate (11–15 mm long), herbaceous, keeled, and 7-veined. Its surface can be smooth or scaberulous, glabrous to pubescent, with a dentate, 2-fid, acute, awned apex (awn 3–15 mm long).

Bromus lanatipes: Distinctive Characteristics

Habit: A perennial species, B. lanatipes is characterized by its woolly butt sheaths and leaf-sheaths. Culms are 40–90 cm long, with pubescent culm-nodes. Leaf-blades are 4–8 mm wide and scabrous.
Inflorescence: It has an open, ovate panicle, 10–25 cm long, with ascending or spreading primary branches.
Fertile Spikelets: Oblong and laterally compressed, these spikelets are 10–30 mm long, with 6–8 fertile florets. They disarticulate below each fertile floret.
Glumes: Glumes are persistent and shorter than the spikelet. The lower glume is lanceolate (1–3-veined, without keels), and the upper glume is lanceolate (3-veined, without keels).
Florets: The fertile lemma is oblong (8–11 mm long), chartaceous, 5-veined, and lacks a keel. Its surface is pubescent, and the apex is awned (awn 2–4 mm long).

Bromus catharticus: Identification Markers

Habit: This perennial, caespitose grass grows 80–100 cm tall, with pubescent leaf-sheaths. Leaf-blades are 10–30 cm long and 3–8 mm wide.
Inflorescence: It features an open, oblong, effuse panicle, 10–40 cm long, with flexuous branches.
Fertile Spikelets: Ovate, strongly laterally compressed, 16–40 mm long and 4–10 mm wide, containing 6–12 fertile florets. Rhachilla internodes are obscured by lemmas.
Glumes: Glumes are persistent and similar. The lower glume is lanceolate (10–15 mm long, 5–9-veined, 1-keeled), and the upper glume is lanceolate (11–17 mm long, 9–13-veined, 1-keeled). Both have an acuminate apex.
Florets: The fertile lemma is oblong (12–20 mm long, 3–7 mm wide), chartaceous, distinctly keeled, and 9–13-veined. Its surface is scaberulous, rough on veins, with a lobed, 2-fid, awned apex (awn 1–9 mm long).

The Diverse Cynodon Genus (Bermuda & Star Grasses)

Cynodon species, including Bermuda grass and star grasses, are well-known for their mat-forming habits and characteristic inflorescences. Let's compare Cynodon nlemfuensis, Cynodon plectostachyus, and Cynodon dactylon.

Cynodon nlemfuensis (Estrella Santo Domingo)

Habit: A mat-forming perennial with stolons but lacking rhizomes. Culms are geniculately ascending, 30–60 cm long. Ligule is a ciliolate membrane (0.3 mm long), and leaf-blades are 5–16 cm long, 2–6 mm wide, often mid-green or glaucous.
Inflorescence: Composed of 4–8(–13) digitate racemes, 4–7(–10) cm long. Spikelets are sessile and 2-rowed, broadside to the rhachis.
Fertile Spikelets: Ovate, strongly laterally compressed, 2–3 mm long, with 1 fertile floret.
Glumes: Persistent, similar, and shorter than the spikelet. Both lower and upper glumes are lanceolate, 1-keeled, and 1-veined, with an acute apex.
Florets: The fertile lemma is ovate, laterally compressed, 2–3 mm long, cartilaginous, keeled, and 3-veined. Its midvein is pubescent or ciliate, and the apex is acute.

Cynodon plectostachyus (Estrella de África)

Habit: Similar to C. nlemfuensis, it's a mat-forming perennial with stolons but no rhizomes. Culms are 30–90 cm long. Ligule is an eciliate membrane (1 mm long), and leaf-blades are 10–30 cm long, 4–7 mm wide, often scabrous.
Inflorescence: Features 7–20 digitate racemes, often in several whorls, incurved, 3–7 cm long. Spikelets are sessile and 2-rowed.
Fertile Spikelets: Ovate, strongly laterally compressed, 2.5–3 mm long, with 1 fertile floret.
Glumes: Persistent, similar, and shorter than the spikelet. Both lower (0.2–0.3 mm long) and upper (0.4–0.6 mm long) glumes are ovate, 1-keeled, and 1-veined, with an acute apex.
Florets: The fertile lemma is ovate, laterally compressed, 2.5–3 mm long, cartilaginous, keeled, and 3-veined. Its midvein is ciliate, and the surface can be glabrous or hispidulous.

Cynodon dactylon (Bermuda Grass)

Habit: A mat-forming perennial with both rhizomes and stolons. Culms are 8–40 cm long. Ligule is a ciliolate membrane (0.2–0.3 mm long), and leaf-blades are 1–12 cm long, 2–4 mm wide, often glaucous.
Inflorescence: Consists of 4–6 digitate racemes, 1.5–6(–8) cm long. Spikelets are sessile and 2-rowed.
Fertile Spikelets: Ovate, strongly laterally compressed, 2–2.5 mm long, with 1 fertile floret.
Glumes: Persistent, similar, and shorter than the spikelet. Both lower and upper glumes are lanceolate, 1-keeled, and 1-veined, with an acute apex.
Florets: The fertile lemma is ovate, laterally compressed, 2–2.5 mm long, cartilaginous, keeled, and 3-veined. Its midvein is pubescent, and the apex is acute.

Paspalum Species: A Morphological Guide

The Paspalum genus includes several pasture grasses with distinct inflorescence and spikelet characteristics. We'll explore Paspalum notatum, Paspalum dilatatum, Paspalum plicatulum, and Paspalum atratum.

Paspalum notatum

Habit: A mat-forming perennial with elongated rhizomes. Culms are 15–50 cm long. Ligule is a fringe of hairs. Leaf-blades are 2–30 cm long, 3–10 mm wide.
Inflorescence: Typically 2(–3) paired, unilateral racemes, 2.5–12 cm long. Spikelets are pedicelled and 2-rowed.
Fertile Spikelets: Elliptic, dorsally compressed, plano-convex, obtuse, 2.5–3.8 mm long, falling entire, with 1 basal sterile floret and 1 fertile floret.
Glumes: The lower glume is absent or obscure. The upper glume is ovate, 1 length of spikelet, cartilaginous, and 3-veined, with an obtuse apex.
Florets: The fertile lemma is ovate, gibbous, 2–3 mm long, indurate, pallid, without a keel. Its surface is striate, and margins are involute.

Paspalum dilatatum

Habit: A caespitose perennial, 40–180 cm tall. Ligule is an eciliate membrane (3 mm long). Leaf-blades are 6–45 cm long, 3–12 mm wide.
Inflorescence: Features (2–)3–5(–11) racemes borne along a central axis, unilateral, 4–11 cm long. Spikelets are in pairs, sessile and pedicelled, 2–4-rowed.
Fertile Spikelets: Ovate, dorsally compressed, plano-convex, acute, 2.8–3.8 mm long, falling entire.
Glumes: Lower glume absent or obscure. The upper glume is ovate, 1 length of spikelet, membranous, yellow, 3-veined, pilose, with ciliate margins and an acute apex.
Florets: The fertile lemma is ovate, gibbous, 2.5–3 mm long, indurate, pallid, without a keel. Its surface is striate.

Paspalum plicatulum

Habit: A caespitose perennial with short rhizomes, 30–120 cm tall. Ligule is an eciliate membrane (2–3 mm long). Leaf-blades are 15–30 cm long, 2–7 mm wide, glabrous or pilose.
Inflorescence: Composed of 2–7 racemes along a central axis, unilateral, 2–15 cm long. Spikelets are in pairs, pedicelled, and 2–4-rowed.
Fertile Spikelets: Elliptic or obovate, dorsally compressed, plano-convex, obtuse, 2.3–3.2 mm long, falling entire.
Glumes: Lower glume absent or obscure. The upper glume is ovate, 1 length of spikelet, membranous, 5-veined, glabrous or puberulous, with an obtuse apex.
Florets: The fertile lemma is ovate, gibbous, 2–3 mm long, indurate, dark brown, without a keel. Its surface is granulose, and margins are involute.

Paspalum atratum

Habit: A robust perennial with elongated rhizomes. Culms are erect or geniculately ascending, 100–150 cm long. Ligule is an eciliate membrane. Leaf-blades are 35–65 cm long, 7–15 mm wide, glabrous or pilose.
Inflorescence: 10–16 racemes along a central axis, unilateral, 3–10 cm long. Spikelets are in pairs and pedicelled, 4-rowed.
Fertile Spikelets: Elliptic or obovate, dorsally compressed, plano-convex, 2–3 mm long, falling entire.
Glumes: Lower glume absent or obscure. The upper glume is elliptic, 1 length of spikelet, membranous, and 5-veined.
Florets: The fertile lemma is elliptic, 2–3 mm long, indurate, dark brown, shiny, without a keel. Its surface is smooth, and margins are involute.

Exploring the Brachiaria Genus

Brachiaria species are often forage grasses with a range of growth habits. Let's compare Brachiaria brizantha, B. decumbens, B. dictyoneura, B. humidicola, and B. ruziziensis.

Brachiaria brizantha

Habit: A caespitose perennial, 30–200 cm tall. Ligule is a fringe of hairs. Leaf-blades are 10–100 cm long, 3–20 mm wide.
Inflorescence: (1–)2–16 racemes along a central axis, unilateral, 4–20 cm long. Spikelets are solitary, sessile, and 1-rowed.
Fertile Spikelets: Elliptic, dorsally compressed, subacute or acute, 4–6 mm long, falling entire. Contains 1 basal sterile and 1 fertile floret.
Glumes: Dissimilar. Lower glume is ovate, clasping, 0.33 length of spikelet, 7–11-veined. Upper glume is oblong, 1 length of spikelet, cartilaginous, 7–9-veined, glabrous or pubescent.
Florets: Fertile lemma is elliptic, 3.5–5.5 mm long, indurate, without a keel, with a granulose surface and involute margins.

Brachiaria decumbens

Habit: A perennial with stolons. Culms are decumbent, 50–150 cm long, wiry. Ligule is a fringe of hairs. Leaf-blades are 5–20 cm long, 7–15 mm wide.
Inflorescence: 2–7 racemes along a central axis, unilateral, 1–5 cm long. Rhachis is broadly winged and ciliate on margins. Spikelets are solitary, sessile, and 2-rowed.
Fertile Spikelets: Elliptic, dorsally compressed, subacute or acute, 4–5 mm long, falling entire. Contains 1 basal sterile and 1 fertile floret.
Glumes: Dissimilar. Lower glume is ovate, clasping, 0.33–0.5 length of spikelet, 9-veined. Upper glume is oblong, 1 length of spikelet, 7-veined, pubescent.
Florets: Fertile lemma is elliptic, 3.5–4.5 mm long, indurate, without a keel, with a granulose surface and involute margins.

Brachiaria dictyoneura

Habit: A caespitose perennial, 40–100 cm long. Ligule is a fringe of hairs. Leaf-blades are linear or lanceolate, 5–30 cm long, 3–10(–30) mm wide.
Inflorescence: 3–8(–12) racemes along a central axis, unilateral, 1–8 cm long. Rhachis is narrowly winged. Spikelets are solitary, sessile, and 2-rowed.
Fertile Spikelets: Elliptic, dorsally compressed, subacute, 4–6 mm long, falling entire. Contains 1 basal sterile and 1 fertile floret.
Glumes: Similar. Lower glume is oblong, 0.75–1 length of spikelet, 11-veined, pubescent. Upper glume is oblong, 1 length of spikelet, 7–9-veined, pubescent.
Florets: Fertile lemma is elliptic, 3.5–5.5 mm long, indurate, without a keel, with a papillose surface and involute margins.

Brachiaria humidicola

Habit: A perennial with stolons. Culms are geniculately ascending or decumbent, 40–100 cm long, rooting from lower nodes. Ligule is a fringe of hairs. Leaf-blades are linear or lanceolate, 4–20 cm long, 3–10 mm wide.
Inflorescence: 2–3(–4) racemes along a central axis, unilateral, 2–7 cm long. Rhachis is wingless or narrowly winged. Spikelets are solitary, sessile, and 2-rowed.
Fertile Spikelets: Elliptic, dorsally compressed, subacute, 4–6 mm long, falling entire. Contains 1 basal sterile and 1 fertile floret.
Glumes: Similar. Lower glume is oblong, 0.75–1 length of spikelet, 11-veined, glabrous or pubescent. Upper glume is oblong, 1 length of spikelet, 5–9-veined, glabrous or pubescent.
Florets: Fertile lemma is elliptic, 3.5–5.5 mm long, indurate, without a keel, with a papillose surface and involute margins.

Brachiaria ruziziensis

Habit: A perennial with short rhizomes. Culms are decumbent, 50–100 cm long, rooting from lower nodes. Ligule is a fringe of hairs. Leaf-blades are lanceolate, 10–25 cm long, 11–15 mm wide, pilose on both sides.
Inflorescence: (3–)5–7(–9) racemes along a central axis, unilateral, 5–10 cm long. Rhachis is broadly winged, foliaceous, and ciliate on margins. Spikelets are solitary, sessile, and 2-rowed.
Fertile Spikelets: Elliptic, dorsally compressed, cuspidate, 4–5 mm long, falling entire. Contains 1 basal sterile and 1 fertile floret.
Glumes: Dissimilar. Lower glume is oblate, clasping, 0.33–0.5 length of spikelet, 11–13-veined. Upper glume is oblong, 1 length of spikelet, 7-veined, pilose.
Florets: Fertile lemma is elliptic, 4.5–5 mm long, indurate, without a keel, with a striate surface and involute margins.

Distinguishing Lolium Species

Lolium, or ryegrass, includes common pasture and turf species. We'll differentiate Lolium multiflorum and Lolium perenne.

Lolium multiflorum

Habit: An annual, caespitose grass, 30–90 cm tall. Leaf-sheath auricles are falcate. Ligule is an eciliate membrane (1–2 mm long). Leaf-blades are 6–25 cm long, 4–10 mm wide.
Inflorescence: A single, bilateral raceme, 10–30 cm long. Spikelets are sessile, appressed, and 2-rowed.
Fertile Spikelets: Oblong, laterally compressed, 7.5–25 mm long, with 5–15 fertile florets. Disarticulation occurs below each fertile floret.
Glumes: The lower glume is absent or obscure. The upper glume is lanceolate, coriaceous, 4–7-veined, without keels, with a smooth surface and obtuse or acute apex.
Florets: The fertile lemma is oblong, 5–8 mm long, coriaceous, 5-veined, without a keel. Its apex is dentate, 2-fid, obtuse, and awned (awn 5–10 mm long).

Lolium perenne

Habit: A perennial, caespitose grass, 30–90 cm tall. Leaf-sheath auricles are falcate. Ligule is an eciliate membrane. Leaf-blades are 3–20 cm long, 2–6 mm wide.
Inflorescence: A single, bilateral raceme, 4–30 cm long. Spikelets are sessile, appressed, and 2-rowed.
Fertile Spikelets: Oblong, laterally compressed, 7–20 mm long, with 4–14 fertile florets. Disarticulation occurs below each fertile floret.
Glumes: The lower glume is absent or obscure. The upper glume is lanceolate, coriaceous, 5–7-veined, without keels, with a smooth surface and obtuse apex.
Florets: The fertile lemma is oblong, 5–7 mm long, coriaceous, 5-veined, without a keel. Its apex is obtuse and muticous (awnless).

Key Grass Morphology Terms for Students

Spikelet: The basic unit of the grass inflorescence, typically consisting of two glumes and one or more florets.
Floret: Consists of a lemma, palea, and the sexual organs (lodicules, anthers, ovary).
Lemma: The lower of the two bracts enclosing the flower in a grass floret.
Palea: The upper of the two bracts enclosing the flower in a grass floret.
Glumes: A pair of bracts at the base of a spikelet.
Awn: A stiff, bristle-like appendage, often found on the lemma or glume.
Keel: A prominent ridge, often found on glumes or lemmas.
Rhizome: An underground stem that produces shoots and roots.
Stolon: A creeping horizontal plant stem or runner that takes root at intervals along its length to form new plants.
Ligule: A small appendage at the junction of the leaf-blade and leaf-sheath.
Panicle: A branched inflorescence where the main axis and secondary axes bear flowers.
Raceme: An unbranched, elongated inflorescence with flowers attached by short pedicels.

Frequently Asked Questions about Grass Identification

What are the main parts of a grass spikelet for identification?

For grass identification, the main parts of a spikelet are the glumes, the fertile florets, and any diminished florets at the apex. The shape, size, compression, vein count, and texture of these components are crucial.

How do rhizomes and stolons help differentiate grass species?

Rhizomes (underground stems) and stolons (above-ground creeping stems) indicate a grass's growth habit. Some species, like Cynodon dactylon, have both, while others, like Cynodon nlemfuensis, only have stolons, and some Brachiaria species may lack both or have short rhizomes.

What is the significance of the lemma and its awn in grass identification?

The fertile lemma's characteristics—such as its shape (ovate, oblong), length, texture (herbaceous, chartaceous, coriaceous, indurate), presence or absence of a keel, vein count, surface features (pubescent, granulose, striate, papillose), and apex (dentate, lobed, awned, muticous)—are highly diagnostic for differentiating grass species, particularly within a genus like Bromus or Lolium.

How does the inflorescence structure vary among different grass genera?

Inflorescence structures vary significantly. Bromus species typically have panicles, while Cynodon, Paspalum, and Brachiaria species commonly exhibit racemes, often arranged along a central axis or in digitate clusters. The number, arrangement, and length of these racemes are key distinguishing features.

What distinguishes Lolium multiflorum from Lolium perenne?

Lolium multiflorum is an annual grass with fertile lemmas that are typically awned (3–15 mm long), while Lolium perenne is a perennial with muticous (awnless) fertile lemmas. Additionally, L. multiflorum spikelets can be slightly longer and contain more florets on average than L. perenne.

Grass Species Morphology and Identification