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CPIE Notebook Project - Grasses and Sedges of Hawai‘i Grass Key – Page 5

Inflorescence of Two or More Racemes or Spikes

panicle of racemes An "inflorescence of racemes" is variously described, but amounts to the primary branches off the culm being racemes that carry the spikelets. Recall (see Fig. 5B, below, right) that in a raceme, each spilkelet is attached to its "branch"—called the rachis—by a short stalk or pedicel. However, in some racemes the pedicels can be very short; indeed. in some genera (e.g., Digitaria), spikelets are paired or grouped with one spikelet attaching directly to the rachis, the other(s) on pedicels.


Figure 5A. The inflorescence of jungle-rice grass
  (Echinochloa colona) showing eight racemes
  branching off the axis (plus one terminal raceme). Only
  two of four rows of spikelets are visible in this view
  showing the rachis (adaxial) side of each raceme.

An inflorescence of spikes will differ from an inflorescence of racemes only in having spikelets without pedicels (see Fig. 4B, middle image). To avoid having to make a distinction (requiring very close inspection of the spikelets) between branches that are spikes and branches that are racemes, this characteristic is not used in the early couplets of our key. All are considered racemose ("simple racemes"). In a few species (an example being California grass), some of the lower racemes may be secondarily branched.

(5B) drawing of several racemes on an axis

In Hawai‘i, our most common racemose inflorescence grasses are:

  • Hilo grass [37]—widespread in wetter areas in the wild and in lawns; TV grass;
  • Narrow-leaved carpet grass [47]—very common small grass, along trails and in lawns;
  • Pitted beardgrass [104]— A very widespread and common small grass;
  • California grass [42]—large grass found on moist soils and around wetlands.
  • Crabgrasses [Digitaria]—weeds in lawns, pastures, and gardens.
  • Grasses in the genus Paspalum—large weeds in lawns, in pastures, and in wet areas.

[INFLORESCENCE SIMPLE RACEMES]

. .
30a (26) Racemes on culm typically two in number, these arising together at end of culm (axis) [31]
30b

Racemes nearly always three or more per culm; if only 2, lower raceme distant from upper on culm

[32]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
31a (30) (5C) close-up of Paspalum raceme Magnifying Lens Spikelets ovate or orbicular (circular) and flattened, approaching disk-like in shape, only slightly longer than wide (Fig. 5C). Paspalum spp.


Figure 5C. Close up of a raceme showing
spikelets (in anthesis) having the flat, nearly
circular shape characteristic of a Paspalum

[36]
31b

Spikelets elongate, not at all disk-like, clearly longer than wide. Racemes usually three in number, the lowest typically reduced in length, or sometimes absent. { A delicate, typically lanky, small grass of lawns and disturbed locations in mesic to wet environmnents. [NAT]

    Digiteria radicosa (J. Presl.) Miq.
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
32a (30) Spikelets with 1 or 2-florets (Fig. 5C): floral bracts usually compacted within a single unit enclosed or nearly so within the largest bract or bract pair. Some florets sterile, imperfect (usually male only), or otherwise much reduced

[33]
32b

Spikelets having several to many florets; floral bracts forming an elongated unit in which the lower bracts (glumes) do not fully enclose the bracts of the upper florets

[37]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
33a (32) Spikelets orbicular to ovate and very flattened (dorsally compressed; see Fig. 5C, above). Plant tufted (clumping). Paspalum spp.

[39]
33b Spikelets either clearly elongate, much longer than wide, upper ends acute (either pointed or blunt) OR spikelets more globose in shape, but then none or only one face flattened (not compressed). Plant tufted or running by stolons [34]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
34a (33) Raceme a tight cluster of three (sometimes just two) spikelets, one sessile the other two on pedicels. Inflorescence elliptical, branches open and somewhat whorled around the axis. { Small, spreading grass, widespread in dry environments, but also appearing in lawns. Manienie ‘ula, golden beardgrass. [IND?]
    Chrysopogon aciculatus (Retz.) Trin.
34b Raceme or spike of many spikelets (exceeding three) [35]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
35a (34) Rachis of raceme a continuous (unjointed) structure, the spikelets attached (singly or in pairs), alternating along two edges of a more or less flattened raceme

[36]
35b (5D) close-up of Ischaemum raceme Racemes 3-4. On backside, rachis of raceme appears as a jointed, thickened and u-shaped structure, with a spikelet on one arm and the next joint above on the other arm (see Figure 5D); a second spikelet is mounted on a very short pedicel or callus arising to front side from insde the base of the u-shaped structure (seen through "pore"). Lower glume smooth and caloused at base, ribbed, rugulose, with 7-8 veins above; tip bifid. Upper glume smooth, but keeled above middle with a few veins; tip prolonged to a sharp point. Bent awns present on some spikelets, these about twice as long as spikelets. { Plant a very hairy, large grass in Hilo area at top of Puainako Street [Nat]
    Ischaemum cf. polystachyum J. Presl.
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
36a (35) Spikelets with awns, these at least as long as length of supporting bractlet

[101]
36b

Spikelets without awns or awns too short to be conspicuous; may have numerous hairs or bristles

[42]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
37a (32) Racemes (spikes) typically two or more arranged somewhat digitally above a separated low spike. Spike typically held out with spikelets on underside of a flattened, somewhat winged rachis [40]
37b

Racemes numerous, these spread out along the culm. Raceme rachis not winged

[48]

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