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CPIE Notebook Project - Key to the Grasses of Hawai‘i Page 6


Key to Genus Paspalum L.

Paspalum spikelets Grass plants attributable to the genus Paspalum are easily spotted in the field, having spikelets of a distinct shape. The inflorescence of a Paspalum (Figure 6B, below) comprises two or more (rarely one) racemes (branches) attached along an axis (culm) rising well above the uppermost leaf blade. Spikelets are attached by short pedicels (stalks), arranged either singly or paired, in two rows along one side (the abaxial face: facing outward or downward) of the flattened rachis. The broadly elliptic to disk-shaped (plano-convex) spikelets (Fig. 6A, right) are distinctive to Paspalum.

panicle of racemes Fourteen species of Paspalum are reported to be present in Hawai‘i (Clayton & Snow, 2010) and many are common in mesic to wet environments, including wetlands. All Paspalum species in Hawai‘i are naturalized species (non-native), except P. scrobiculatum (mau‘u laiki)—a southeast Asian species distributed across the Pacific Islands—is possibly indigenous or a very early Polynesian introduction.

Once you are comfortable recognizing an unknown grass by the spikelet shape as a Paspalum, you can start the key at the first couplet below.

Figure 6A. The inflorescence of Dallis grass
  (Paspalum dilatatum) showing four
  racemes branching off the axis. The 2nd
  raceme from the top is hidden behind the 3rd.
  Inset is a closeup of the discoid spikelets crowded
  along one side of the rachis.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
35a Racemes nearly always just two in number (rarely three or more). Creeping perennials [36]
35b

Racemes nearly always three or more per culm. Tufted (clumping) annuals or perennials

[39]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
36a (31) & (35) Plant spreading by stolons (stems growing horizontally outward and rooting at nodes). Ligule an eciliate membrane. [37]
36b

Plant spreading by underground "rootstock" (rhizomatous). Racemes 2(-3). Spikelet broadly elliptic, plump, 2.5-3.8 mm long. Ligule a fringe of hairs { Small lawn grass. Bahia grass. [NAT]

Paspalum notatum Flüggé
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
37a (36) Wild Hilo grass Racemes thin to 2.5 in (10 cm) each, widely spreading, resembling an old TV "rabbit ears" antenna. Spikelets minute, under 0.1 in (2 mm) in length. { Common small, spreading grass found in the wild and a lawn grass mostly in wet, windward areas. Hilo grass, mau‘u Hilo. [NAT]
Paspalum conjugatum Bergius
37b

Racemes robust. Spikelets >0.1 in (3 to 4.5 mm) long

[38]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
38a (37) Leaf blades stiff, conspicuously distichous (leaves appear two-ranked) towards upper end. Racemes erect, spreading as they mature, although infrequently flowering; most culms sterile. Culms and leaves without hairs except perhaps for a ring at the truncate, membranous ligule. { Plants growing along the margins of estuarine waters and coastal wetlands, often forming dense, dark green stands bordering the waters' edge. The inflorescence and absence of hairs distinguishes it from the similar-appearing native coastal grass, ‘aki‘aki. Seashore paspalum [NAT]
Paspalum vaginatum Sw.
38b

Leaf blades conspicuously alternate up the culm. Racemes, short erect, spikelets elliptic. Leaf sheath, ligule, and node densely hairy. { Spreading perennial in wetlands and wet soils. Knotgrass. [NAT]

Paspalum distichum L.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
39a (33) & (35) Close-up of P. fimbriatum spikelets Spikelets fringed with a broad, ragged or lacerate (much cut) margin. Leaves broad, distinctly wavy; ligule a fringe of hairs. { Medium size, annual, clumping grass in mesic to wet areas; often a weed in lawns. Panama grass, fimbriate paspalum. [NAT]
Paspalum fimbriatum Kunth

Figure 6C. Close-up of spikelets of Panama grass with lacerate wing of 1st lemma of one spikelet outlined in black. Note also, prominent midnerve prolonged beyond apex of each lemma (bract).

39b

Spikelets fringed with hairs (ciliate or pubescent) or bare (glabrous), but lacking a surrounding ragged wing. Leaves, if broad, not wavy; ligule an eciliate membrane.

[40]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
40a (39) Magnifying Lens Spikelets with long, stiff hairs (ciliate) along margins of upper glume. [41]
40a Spikelets not ciliate (lacking long hairs); spikelets either smooth and hairless (glabrous) or with fine, short hairs (puberulent) or sparsely woolly along margin of glumes. [42]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
41a (40) Racemes less than 10 (typically 3 to 7). Spikelets measure more than 0.1 in (2.8 - 4 mm) in length. { Medium size, fairly common grass in wet to dry areas, sometimes a coarse weed in lawns. Dallis grass. [NAT]
Paspalum dilatatum Poir
41b

Racemes more than 10. Spikelets measure less than 0.1 in (2 - 2.8 mm) in length. { Medium size grass in wet areas, sometimes in or near flowing streams. Vasey grass. [NAT]

Paspalum urvillei Steud.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
42a (40) Spikelets in pairs on each side of rachis midrib, borne on short pedicels (one slightly longer than the other), forming four rows of spikelets (NOTE: if only two rows, then pedicel evident indicating missing spikelet of each pair or rows very untidy). Glumes puberulent, sparsely woolly, or lacking hairs altogether. [43]
42b

Only one spikelet present on each side of midrib, forming two, closely imbricate rows of spikelets. Spikelets without hairs (glabrous), broadly elliptic in outline, greater than 1/16 in (2.0-2.5 mm) in length; floret light brown. Racemes widely spaced, 4 to 6 per culm. Leaf blades narrow, under 1/2 inch (12 mm) across, mostly without hairs (glabrous).{ Perennial, tufted medium-size grass growing on thin, poor soils or in wetland soils. Ricegrass, ditch millet, mau‘u laiki. [?IND]

Paspalum scrobiculatum L.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
43a (42)

Racemes few, typically 1 to 10 (-15). Spikelets greater than 1/16 in (1.4 mm) long.

[44]
43b Racemes very numerous, ten to as many as 60, these purplish to brownish tinged and crowded on the axis. Spikelets about 1/16 in (1.3-1.4 mm) in length, suborbicular, puberulent, plump; floret pale. { Perennial, medium size, coarse grass in wet areas. No common name in Hawai‘i. [NAT]
Paspalum paniculatum L.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
44a (43)

Racemes typically 5 to 10(-15). Spikelets puberulent or woolly on margins, nearly 1/8 in (2 to 2.7 mm) in length; floret yellow. Leaf blades mostly over 1 ft (30 cm), up to 1 in (2.5 cm) wide; culms 2-6 ft (70-200 cm) long. { Perennial, medium size, coarse grass forming substantial tufts in open field in mesic locations. [NAT]

Paspalum macrophyllum Kunth
44b

Racemes typically 1 or 2(-5). Spikelets glabrous on margins, less than 1/8 in (1.4 to 2.6 mm) in length. Leaf blades mostly well under 1 ft (30 cm) in length, up to 3/4 inch (2 cm) wide; culms 1-3 ft (30-90 cm) long. { Perennial, medium size grass. [NAT]

Paspalum setaceum Michx.


Species of Paspalum reported to be in Hawai‘i
  but not covered in this key; and some synonyms:

    P. commersonii Lam. (=P. scrobiculatum)
    P. longifolium Roxb.
    P. malacophyllum Trin.
    P. orbiculare G. Forst. (=P. scrobiculatum)
    P. virgatum L.
     

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