Although the reduced flowers seem well adapted for wind pollination, some are cleistogamous in certain species, and some (e.g., P. lanceolata) are in part insect-pollinated.
1. Plant with several pairs of opposite linear cauline leaves, annual without a basal rosette, the stem often branched.
1. Plant with leaves all basal or nearly so, the stem very short and unbranched (though several scapes may arise from a rosette).
2. Bracts of inflorescence pubescent or puberulent across the back, at least toward their base.
3. Mature bracts (at least the lower ones) (2–) 3–10 (–12) times as long as the calyx.
3. Mature bracts scarcely if at all longer than the calyx.
4. Corolla lobes widely spreading at maturity; pubescence at middle of scape strongly ascending or appressed, the hairs (as in the spike) not septate; leaves linear-lanceolate.
4. Corolla lobes erect, appearing beak-like over the fruit; pubescence at middle of scape spreading, the hairs (as also in the spike) septate; leaves narrowly lanceolate to elliptic.
2. Bracts of inflorescence glabrous or at most ciliate.
5. Bracts with broad scarious margins occupying more than half their area, ovate and at least the lower ones ± acute-acuminate; scapes deeply furrowed and ridged; calyx with the 2 sepals beneath the bract connate, the other 2 sepals distinct; leaves (including obscurely differentiated petiole) (2.5–) 6–21 times as long as broad.
5. Bracts with scarious margins occupying less than half their area, of various shape; scape terete or at most weakly ridged; calyx with all 4 sepals distinct; leaves less than 3 times as long as broad or if longer, then including a definite long petiole.
6. Leaf blades flat on the ground, pubescent on both surfaces, tapering into rather indistinct and short petioles; bracts ovate.
6. Leaf blades ± ascending, glabrous or slightly pubescent, abruptly tapered to cordate at the base, on definite long petioles; bracts linear to ovate.
7. Older leaf blades often ± cordate, the principal longitudinal veins, although basal, closely paralleling the midvein before diverging (hence, with pinnate aspect); bracts broadly ovate; plant of wet places (typically a streambed in rich forests), blooming in May (–early June), completely glabrous; major roots large and fleshy (5 mm or more thick).
7. Older leaf blades broadly tapered to truncate at base, the principal longitudinal veins all clearly diverging from the base; bracts various; plant of dry to moist places, blooming June–August, often pubescent on scape and/or leaves; major roots fibrous.
8. Capsule plumply ovoid (shaped like a fat acorn), dehiscing about the middle; bracts nearly obtuse to rounded (though sometimes with a hyaline apiculus), broadly ovate, less than twice as long as broad.
8. Capsule narrowly ellipsoid-oblong, dehiscing distinctly below the middle; bracts ± sharply acute, lanceolate, ca. 2–3 times as long as broad.