Key to Wisconsin Cerastium

• 1a.Stems, leaves, and sepals densely covered in white tomentose hairs C. tomentosum

• 1b.Stems, leaves, and sepals covered with straight or irregular hairs, not white, sometimes glandular 2

• 2a.Leaves usually with axillary clusters of leaves present; leaf blades linear to narrowly oblong or lanceolate; petals showy, 2–3 times as long as the sepals; anthers 0.8–1.1 mm long 3

• 2b.Leaves without axillary clusters of leaves present; leaf blades narrowly to broadly ovate to elliptic; petals shorter than the sepals or barely longer; anthers less than 0.7 mm long 4

• 3a.Cauline leaves all similar in size and shape (except the most basal ones); mid-cauline leaves 0.5–3 mm wide, apex acute (rarely obtuse); petals 7.5–12.5 mm long C. arvense

• 3b.Cauline leaves largest at mid-stem, those at the distal and proximal ends smaller in size; mid-cauline leaves 3–6 mm wide, apex obtuse; petals 10–15 mm long C. velutinum

• 4a.All inflorescence bracts completely herbaceous, glandular-puberulent even at the tips; pedicels often distinctly arched below the calyx 5

• 4b.Distalmost inflorescence bracts with narrow to broad scarious margins at the tips, the tips glabrous or sometimes with a few non-glandular hairs; pedicels slightly if at all curved 6

• 5a.Leaves less than 1 cm long, apex obscurely acute; pedicels equaling or shorter than the capsules, deflexed proximally C. brachypodum

• 5b.Leaves 1 cm or longer, apex distinctly acute to acuminate; pedicels much longer than the capsules, deflexed distally C. nutans

• 6a.Plants covered in eglandular hairs, rarely with glandular hairs; sepals lacking or rarely with sparse glandular hairs; petals deeply cleft, almost to their bases; stamens 10 C. fontanum

• 6b.Plants covered in both glandular and eglandular hairs; sepals glandular-pubescent; petals shallowly notched; stamens 5 7

• 7a.Bracts and sepals scarious for, at most, the apical 1/4; petal veins forked; seeds covered with acute to blunt papillae C. pumilum

• 7b.Bracts and sepals scarious for at least the apical 1/3; petal veins unforked; seeds smooth or with small, rounded papillae C. semidecandrum