The number of styles and hence of capsule teeth (the same number or, when teeth split, twice the number of the styles) may vary from the “typical,” making absolute reliance on this key character less trustworthy than one would like. The nature of the inflorescence is also variable, as well as difficult to describe simply. Silene pendula L., a native of the Mediterranean region, was collected once at Lansing in 1887 as “Escaped from flower garden” (MSC). A specimen of Silene flos-cuculi (L.) Greuter & Burdet was obtained by an unknown collector from "Farm Flats" in Lansing (Ingham Co.) in 1885, perhaps from cultivated plants.
1. Calyx glabrous.
2. Plant an annual, usually with glutinous zones on upper internodes; petals absent or tiny and pink to rose; calyx with 10 prominent nerves.
2. Plant a perennial without glutinous zones on the stem; petals white; calyx with 20 nerves, at least at base, but these often obscure and anastomosing.
3. Mature calyx little if at all inflated around the capsule, without conspicuous anastomosing veins, ± tapered to base; upper bracts of inflorescence minutely ciliate; stalk of capsule (and ovary) minutely puberulent, ca. 1.5 mm long.
3. Mature calyx much inflated around the capsule, usually with conspicuous anastomosing veins, umbilicate at base (the pedicel attached in a dimple); upper bracts of inflorescence only very rarely ciliate; stalk glabrous, ca. 1.5–3.5 mm long.
1. Calyx pubescent.
4. Leaves whorled (except at uppermost and lowermost nodes); petals deeply fringed (more than once cleft).
4. Leaves all opposite; petals at most once-cleft.
5. Plant densely white-woolly.
5. Plant glabrate to variously hairy, but never white-woolly.
6. Flowers crowded in a dense, flat-topped inflorescence, usually numerous.
6. Flowers in loose racemes, or open cymes, never crowded, few to many.
7. Calyx with ca. 30 prominent straight raised nerves.
7. Calyx with at most ca. 20 nerves, these often obscure.
8. Petals bright red, cleft into two lance-acute lobes (± rounded at tips).
8. Petals white to cream or pink, the lobes ± obtuse and broadly rounded.
9. Lower inflorescence bracts nearly as large as the upper cauline leaves, the flowers thus appearing to be solitary in the leaf axils; stems puberulent with short, incurved hairs or essentially glabrous.
9. Lower inflorescence bracts much smaller than the upper foliage leaves; stems with straight, spreading or slightly reflexed hairs.
10. Flowers in 1-sided spikes or racemes, the inflorescence simple or dichotomously once- or twice-forked and the flowers or flowering branches 1 per node; calyx ca. 10.5–13.5 (–15) mm long.
10. Flowers in a panicle or compound cyme scarcely if at all 1-sided, the inflorescence typically bearing opposite branches, with flowers (or branches) thus 2–3 per node; calyx 11–27 mm long (except in S. nutans, which has distinctive tufts of spatulate leaves at base).
11. Calyx ca. 10 mm long or shorter; plant a perennial with mostly basal leaves and vegetative tufts of narrowly spathulate leaves ca. 5–15 mm wide at base.
11. Calyx 11–27 mm long; plant an annual, a biennial, or a short-lived perennial, without basal tufts of leaves (or these basal leaves mostly elliptic and ca. 15–30 mm wide if present).
12. Petals clear pink; inflorescence bracts, upper part of stem, and calyx with spreading pubescence, but essentially lacking capitate glands.
12. Petals white or very pale pinkish tinged; inflorescence bracts, upper part of stem, and calyx with ± dense pubescence and numerous capitate glands.
13. Lobes of calyx 6–11 mm long, not over 1 mm wide at middle; total calyx length 20–27 mm; plants with bisexual flowers; styles 3, the capsule opening by 6 teeth, these strongly recurved at maturity; upper internodes clammy-viscid in living plants, with ± dense glands sessile or on short hairs, the longer hairs mostly not gland-tipped.
13. Lobes of calyx 2.5–6 (–7) mm long, if as long as 6–7 mm then at least 1 mm wide at middle; total calyx length (11–) 14–22 (–27) mm; plants dioecious, the flowers of pistillate plants with 5–6 (often more, rarely fewer) styles, the capsule opening by twice as many teeth, these at most spreading; upper internodes not clammy-viscid to the touch when fresh, with glands as frequent on tips of longest hairs as on shorter ones (and usually less dense than in preceding species).