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CPIE Notebook Project - Grasses and Sedges of Hawai‘i Grass Key – Page 14

Paniculate Inflorescences

sugar cane panicle

A panicle is an inflorescence type characterized by spikelets on small stalks called pedicels that are attached to branches coming off the culm or axis. Depending upon branch length and spreading of the branches, a panicle can be open or closed to varying degrees, and the shapes of paniculate inflorescences show wide variation. Identifying these grasses starts with recognizing the basic overall shape of the inflorescence, then considering details of the branching and the spikelets.

Figure 14A An open panicle of commercial sugar
  cane, a hybrid Saccharum officinarum. Overall
  shape of inflorescence is ovoid.

Be aware, that in some grasses, the panicle branches can be pressed against the culm (termed appressed) to form a closed or contracted panicle, then these branches spread open at anthesis (the stage at which the anthers emerge from the enclosing bracts of the floret). Inflorescences with short branches and close-packed spikelets are called spike-like panicles and are covered in the key starting below at couplet [80].

Guinea grass inflorescence

An inflorescence like that shown in Fig. 14B (on right) can be interpreted as a panicle of racemes (recall far right drawing in Fig. 4B). The key should work whichever choice is made.

Figure 14B. An open panicle of Guinea grass
  (Megathyrsus maximus). Overall shape of this
  inflorescence is ovoid.

Our most common open paniculate inflorescences are found on:


. .
80a (21) Inflorescence more or less contracted: shape spike-like (very short branches), or cylindrical (short, even branches), or a spindle or very narrowly ovoid (oblong), OR shape difficult to ascribe to a simple geometric form (for example, spikelets clustered forming lobes on branches mostly in one plane; infloresence shape very crudely triangular). [81]

Inflorescence very open, overall shape tending to ovoid (see Figs. 14A and 14B, above) or some other broadly rounded shape

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81a (80) Inflorescence cylindrical, narrowing down only at the top end, the branches and spikelets crowded around a central axis or tightly appressed to the central axis [88]

Inflorescence shape other than cylindrical: somewhat open and oblong, pyramidal, broom- or fan-like, or difficult to describe

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82a (80) Inflorescence silky and/or plumose due to spikelets having an abundance of thin, usually white, bristles [89]

Inflorescence not silky; spikelets without silky bristles

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83a (82) Most spikelets with one or more conspicuous awns extending well beyond the spikelet [102]

Spikelets without conspicuous awns; if awns present, these are short, no longer than bract to which they are attached

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Example of 2-floret spikelets Example of multiple florets per spikelet

Figures 14C and 14D. Floret counts: (left) panicle of 2-flowered spikelets (Sorghum
) in which lemma of second floret is awned; (right) a panicle of spikelets
   with multiple florets (Bromus catharticus).

84a (83) Spikelets mostly of one or two florets, but no more than three (see Fig. 14C, left above) [85]

Spikelet of multiple florets (more than two; as in Fig. 14D, right above). Ligule membranous

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85a (84) Spikelets about 2.8 mm (1/10 in) long, single at the tips of long, three-sided, scabrous branches; spikelets spindle-shaped, not or hardly compressed. Glumes unequal, the lower glume clasping and much shorter than spikelet [94]

Spikelets somewhat compressed, oblong in outline, upper or both glumes exceed lemmas

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87a (85) Magnifying Lens Inflorescence open, or closing after anthesis; spikelets crowded and tight against the rachis, each set on a conspicuous, cylindrical callus (base attached to rachilla). Spikelets compressed, covered by short hairs. Glumes together enclosing floret. Ligule may be very long (5 to 8 mm). { Perennial, small to moderate in size, spreading by stolons; culms typically decumbant (laying out flat). Found in disturbed, usually wet, sites. Creeping bent grass, marsh bent. [NAT]
    Agrostis stolonifera L.

Inflorescence open. Spikelets not or only slightly compressed, generally round in cross-section, without hairs (glabrous) or, if grass of moderate (not large) size, covered with fine hairs. First glume short but conspicuous, surrounding the base of the spikelet.

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88a (81) Spikelets of one or two florets. Foxtails, rattails, or similar [said 41(5), not 23(4)?] [23]

Spikelet of multiple florets (more than two; see Fig. 14C above). Ligule a membrane, without cilia

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89a (84)
Spikelets with fewer than 10 florets, these loosely imbricate (overlapping; rachilla visible in some spikelets) and only weakly compressed laterally; florets with or without awns. Inflorescence shape tending to pyramidal

89b Spiklelets typically with more than 6 florets and up to 40 in some species; spikelets with florets usually tightly imbricate and compressed laterally, without awns or with very short awns. Inflorescence shape variable.

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90a (89) Lemmas with short awns. Culms compressed. Spikelets 2-4 flowered, purplish. {Medium perennial forming dense sod above 4000 ft (1200 m). Kentucky bluegrass. [NAT]
    Poa pratensis L.

Lemmas without awns, tip obtuse, margins membranous towards tip, with five nerves and curled hairs. purplish. {Small annual in typically dry to mesic sites, forming weak mats at best, growing over a wide elevation range. Annual bluegrass [NAT]

    Poa annua L.
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91a (89) Spikelets with more than 10 florets or if florets fewer than 10, then spikelets tiny, under 0.08 in or 2 mm across; Inflorescence shape tending to ovoid or columnar, or even spike-like. Eragrostis spp.

91b Bromus spikelets Florets 6-12 per spikelet, spikelets >1/4 in or 5 mm across, strongly compressed laterally, the lemmas sharp tipped or short-awned; Glumes shorter than spikelet, similar, about 1 cm (3/8 in) long, lower the shorter of the two. Annual. Rescue grass. [Nat]
    Bromus catharticus Vahl

Figure 14E. Lower spikelets of B. catharticus. Note glumes have turned brown as the inflorescence has dried.
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94a (85) Magnifying Lens Panicle very open at maturity, ovoid in overall shape (see Fig. 14B), the lowest branches up to 40 cm long and typically whorled. Spikelets blunt tipped, with or without covering of fine hairs. First glume hyaline at margins, 1/4 to 1/3 length of spikelet, tip obtuse (rounded). Second glume as long as spikelet, 5-nerved. Fertile floret transversely rugose (ridged cross-wise; remove second glume to view) [95]

Panicle branches held more verticle, lowest branches not whorled, overall shape not obvious. Spikelets glabrous, elongated and acute at tip. Lower glume ~1/5 to 1/3 length of spikelet, obtuse, even truncate, hyaline. Second glume as long as floret, 7-9-nerved. Surface of fertile floret white, network-like. { Perennial, with rhizomes; in moist, disturbed environments. Torpedo grass, quack grass. [Nat]

    Panicum repens L.
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95a (94) Magnifying Lens Spikelets without hairs (glabrous). Plants typically 4 to 9 ft (70 - 300 cm) tall, very robust; leaf blades on mature plants up to 1 in (3 cm) across. { An extremely common, clumping grass in lowland disturbed areas and pastures, especially mesic and wet areas. Stems have stiff hairs that can cause itching as hairs detach and irritate the skin. A highly variable species with respect to size. Guinea grass. (Fig. 14B) [NAT]
    Megathyrsus maximus (Jacq.) B.K. Simon & W.L. Jacobs

Spikelets sparsely covered with short hairs. Plants ~3 ft or less in height (including inflorescence); leaf blades on mature plants less than 1/2 in (1.5 cm) across. { Clumping but not especially robust. Common in lowland disturbed areas and pastures, especially in dry areas. Guinea grass (short type), green panic. Widely considered a synonym of M. maximus. [NAT]

Megathyrsus maximus var trichoglume (K. Schum.) C. E. Hibberd

Synonyms for species on this page:

    Bromus willdenowii Kunth (= B. catharticus)
    Panicum maximum Jacq. (= Megathyrsus maximus)
    Urochloa maxima (Jacq.) Webster (= Megathyrsus maximus)

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