CHAPTER VI.
Series I—Panicaceæ.
TRIBE I—PANICEÆ.
This is a fairly large and important tribe flourishing mostly in the warm regions and the tropics. It is very well represented in South India and fifteen genera are met with.
The inflorescence varies very much within this tribe and consists of spikes, racemes and panicles. The spikelets are usually four-glumed and contain one terminal perfect flower and a staminate or neutral flower below. But in the genus Isachne both the flowers are perfect. In some grasses the spikelets contain only staminate or pistillate flowers. In Coix and Polytoca the plant bears both male and female spikelets in the same inflorescence, but in Zea on the same plant they occur as distinct inflorescences. The littoral grass Spinifex is diœcious.
The first glume of the spikelet is the smallest. In Panicum it is nearly two-thirds or less than the third glume. It is very small in Digitaria and entirely suppressed in Paspalum. In Eriochloa it is reduced to a minute ridge lying just close to the swollen ring-like joint of the rachilla. The second and the third glumes are more or less equal and similar in texture. The fourth glume becomes firm and rigid along with its palea and usually encloses the grain.
The pedicel is jointed in some genera and in others it is continuous with the spikelet and not jointed. When mature the spikelets fall away either by themselves, singly with their pedicels or in groups with portions of rachis, according to the position of the joint. Bristles (branchlets) are often found on the pedicels. In Setaria a few are borne by the pedicels. The bristles form a regular involucre at the base of a group of spikelets in Pennisetum, and in Cenchrus these become united at the base into a mass forming a kind of burr around the spikelets.
KEY TO THE GENERA.
- A. Spikelets articulate on their pedicels.
- B. Spikelets without involucels.
- C. Spikelets dorsally flattened, awnless.
- Inflorescence racemed; glumes three; nerves of second glume five or less, side nerves curved 1. Paspalum.
- Inflorescence digitate; glumes three with a minute glume; nerves of second glume five to seven, straight and prominent 2. Digitaria.
- Inflorescence panicled; glumes three with a thickening at the base of the spikelet 3. Eriochloa.
- Inflorescence racemed or paniculate; glumes four, first two glumes unequal 4. Panicum.
- Inflorescence panicled, branches of panicle produced beyond the uppermost spikelet; glumes four, the first being minute and hyaline 5. Chamæraphis.
- Spikelets unisexual and diœcious 6. Spinifex.
- CC. Spikelets awned.
- Glumes four, second glume broadly fimbriate with hairs; palea of the third glume short and deeply cleft, fourth glume awned 7. Axonopus.
- C. Spikelets dorsally flattened, awnless.
- BB. Spikelets involucellate 8. Setaria.
- B. Spikelets without involucels.
- AA. Spikelets not jointed but continuous.
- Spikelets in involucelled deciduous fascicles.
- Involucre of bristles free 9. Pennisetum.
- Involucre of bristles united 10. Cenchrus.
- Spikelets in involucelled deciduous fascicles.