Understanding grass morphology and species identification is crucial for anyone studying botany, agriculture, or ecology. This comprehensive guide will break down the key characteristics used to distinguish various grass species, offering a foundational understanding of their unique features.
From the overall growth habit to the intricate details of their florets, each part of a grass plant tells a story about its identity. Mastering these morphological distinctions is essential for accurate species identification, whether for academic study or practical application.
Unveiling Grass Morphology and Species Identification: An Overview
Grass morphology refers to the study of the physical form and structure of grasses. Species identification relies on observing and comparing specific attributes, including their habit (how they grow), leaf characteristics, inflorescence (flower arrangement), and the detailed structure of their spikelets and florets. These attributes help differentiate between genera like Brachiaria, Cynodon, Bromus, Lolium, and Paspalum.
Brachiaria Species: A Detailed Look
The genus Brachiaria includes several important species, each with distinct morphological features. Let's explore some key examples:
Brachiaria ruziziensis:
- Habit: Perennial, decumbent culms (50–100 cm long, 3–4 mm diam.), rooting from lower nodes. Short rhizomes. Ligule is a fringe of hairs.
- Leaves: Lanceolate leaf-blades (10–25 cm long, 11–15 mm wide), pilose surface (hairy on both sides), cartilaginous margins.
- Inflorescence: Composed of (3–)5–7(–9) unilateral racemes (5–10 cm long) along a central axis (4–12 cm long). Rhachis is broadly winged (2–3.5 mm wide), foliaceous, with a rounded midrib, ciliate on margins. Spikelets are adaxial, 2-rowed, solitary, and sessile.
- Spikelets: Elliptic, dorsally compressed, cuspidate, 4–5 mm long, falling entire. Comprising 1 basal sterile floret (male, with palea) and 1 fertile floret. Glumes are dissimilar, reaching the apex of florets. Lower glume oblate, 0.33–0.5 length of spikelet, 11–13-veined, obtuse apex. Upper glume oblong, 1 length of spikelet, 7-veined, pilose surface, acute apex. Fertile lemma is elliptic, 4.5–5 mm long, striate surface, involute margins, apiculate apex. Palea is involute.
Brachiaria brizantha:
- Habit: Perennial, caespitose, erect or geniculately ascending culms (30–200 cm long). Ligule is a fringe of hairs.
- Leaves: Linear or lanceolate leaf-blades (10–100 cm long, 3–20 mm wide).
- Inflorescence: (1–)2–16 unilateral racemes (4–20 cm long) along a central axis (3–20 cm long). Rhachis narrowly winged, semiterete, ciliate on margins. Spikelets adaxial, 1-rowed, solitary, sessile.
- Spikelets: Elliptic, dorsally compressed, subacute or acute, 4–6 mm long. Glumes dissimilar. Lower glume ovate, 0.33 length of spikelet, 7–11-veined, obtuse or acute apex. Upper glume oblong, 1 length of spikelet, cartilaginous, 7–9-veined, glabrous or pubescent surface, obtuse or acute apex. Fertile lemma elliptic, 3.5–5.5 mm long, granulose surface, acute apex.
Brachiaria decumbens:
- Habit: Perennial, decumbent culms (50–150 cm long). Stolons present. Ligule is a fringe of hairs.
- Leaves: Linear or lanceolate leaf-blades (5–20 cm long, 7–15 mm wide).
- Inflorescence: 2–7 unilateral racemes (1–5 cm long) along a central axis (1–8 cm long). Rhachis broadly winged.
- Spikelets: Elliptic or obovate, dorsally compressed, plano-convex, 2–3 mm long. Upper glume elliptic, 1 length of spikelet, 5-veined. Fertile lemma elliptic, 2–3 mm long, dark brown, smooth surface.
Brachiaria dictyoneura:
- Habit: Perennial, caespitose culms (40–100 cm long) without nodal roots. Ligule is a fringe of hairs.
- Leaves: Linear or lanceolate leaf-blades (5–30 cm long, 3–10(–30) mm wide).
- Inflorescence: 3–8(–12) unilateral racemes (1–8 cm long) along a central axis (5–25 cm long). Rhachis narrowly winged. Spikelets adaxial, 2-rowed, solitary, sessile.
- Spikelets: Elliptic, dorsally compressed, 4–6 mm long. Glumes similar, reaching apex of florets. Lower glume oblong, 0.75–1 length of spikelet, 11-veined, pubescent surface, obtuse or acute apex. Upper glume oblong, 1 length of spikelet, 7–9-veined, with cross-veins, pubescent surface, obtuse apex. Fertile lemma elliptic, 3.5–5.5 mm long, papillose surface, obtuse or apiculate apex.
Brachiaria humidicola:
- Habit: Perennial, geniculately ascending or decumbent culms (40–100 cm long), rooting from lower nodes or without nodal roots. Stolons present. Ligule is a fringe of hairs.
- Leaves: Linear or lanceolate leaf-blades (4–20 cm long, 3–10 mm wide).
- Inflorescence: 2–3(–4) unilateral racemes (2–7 cm long) along a central axis (2–13 cm long). Rhachis wingless or narrowly winged. Spikelets adaxial, 2-rowed, solitary, sessile.
- Spikelets: Elliptic, dorsally compressed, 4–6 mm long. Glumes similar. Lower glume oblong, 0.75–1 length of spikelet, 11-veined, glabrous or pubescent surface, obtuse apex. Upper glume oblong, 1 length of spikelet, 5–9-veined, with cross-veins, glabrous or pubescent surface.
Identifying Cynodon Species by Morphology
Cynodon species, commonly known as