THE GRASSES OF BRITISH HONDURAS AND THE PETEN, GUATEMALA 167

 S Culms widely spreading at base, geniculate, elongate;
 spikelets arranged on one side of spikelike racemes- .. 3. P. purpnrascens
 Fruit smooth.
 Creeping rhizomes present.---..- 7. P. altmm
 Creeping rhizomes wanting.
 Spikelets glabrous (see also P. tuerckheimii).
 First glume broadly triangular, not more than one-
 fourth as long as the spikelet.__.... ... ..... 4. P. aquaticum
 First glume acute, two-thirds as long as the spikelet 6. P. ichnanthoides
 Spikelets pubescent, sparsely hispid, or sparsely pilose.
 Spikelets acuminate, sparsely pilose 33. P. tuerckheimii
 Spikelets acute.
 Spikelets pubescent; first glume two-fifths as long
 as the spikelet; usually obtuse, glabrous; plants
 slender ..... 23. P. fusiforme
 Spikelets sparsely hispid; first glume acute, three-
 fourths as long as the spikelet; plants coarse,
 robust ._. 32. P. rudgei
Spikelets not more than 2 mm. long.
 Spikelets short-pedicellate, arranged on one side of spikelike
 racemes.
 Blades lanceolate or ovate-lanceolate; culms creeping,
 rooting at the nodes.
 Fruit transversely rugose ._ _.. 2. P. reptans
 Fruit smooth.
 Sterile lemma with 2 prominent crateriform glands... 14. P. pulchellum
 Sterile lemma not glandular .. .15. P. frondescens
 Blades linear.
 Rachis of racemes pilose; branchlets very short or wanting.
 Panicles more than 25 cm. long .10. P. milleflorum
 Panicles not more than 15 cm. long _. .. 9. P. pilosum
 Rachis of racemes not pilose; short branchlets usually
 numerous.
 Nodes glabrous.
 Blades narrowed at the base-.- -- .11. P. laxum
 Blades cordate at the base.-__...-.._. -12. P. boliviense
 Nodes pubescent .- 13. P. polygonatum
 Spikelets paniculate.
 Panicles small, contracted, few flowered, on slender leafless
 branches from the upper nodes ......._ 8. P. stenodoides
 Panicles open, often large, many flowered, terminal on the
 main culm or leafy branches.
 First glume half as long as the spikelet or longer.
 Spikelets not more than 1.5 mm. long.
 Spikelets glabrous; blades 2 to 6 mm. long, glaucous.
 Culms erect; blades 3 to 6 cm. long, glabrous 21. P. cyaneecens
 Culms decumbent, spreading; blades 1.5 to 2.5 cm.
 long, often pilose__.. .. 20. P. parvifolium
 Spikelets papillose-hirsute; blades thin, 8 to 15 mm.
 wide 34. P. hirtum
 Spikelets IS to 2 mm. long ..-- ... 19. P. bartlettii
 First glume much less than half as long as the spikelet.
 Culms widely spreading, freely branching.
 Culms viscid below the nodes; spikelets 2 mm. long.31. P. viscidellum
 Culms not viscid below the nodes; spikelets not more
 than 1.5 mm. long.
 Spikelets glabrous.
 Panicles 10 cm. long; fruit sparsely silky..... ...... 16. P. schiffneri
 Panicles 20 to 30 cm. long; fruit glabrous. .- 18. P. trichanthtim