Stellaria

1. Leaves (at least the middle and lower ones) with broadly ovate blades and distinct petioles.

2. Sepals mostly 4.5–5 mm long; seeds 0.9–1.3 mm wide, dark brown.

S. media

2. Sepals mostly 3–4 mm long; seeds 0.5–0.9 mm wide, yellowish-brown.

S. pallida

1. Leaves linear to lanceolate, without petioles.

3. Bracts on middle (and lower) portion of inflorescence green, herbaceous; principal leaves ca. 4.5–7 times as long as broad; sepals ca. (1.5–) 2–3.5 mm long, even in fruit.

4. Leaves ± sparsely ciliate, at least toward the base, the principal ones 15–35 (–40) mm long; petals absent or (rarely) nearly equaling the sepals.

S. borealis

4. Leaves completely glabrous, less than 12 (–18) mm long; petals exceeding the sepals.

S. crassifolia

3. Bracts on middle (and usually lower) portion of inflorescence scarious (at most with green midrib); principal leaves often more than 8 times as long as broad; sepals often longer (especially in fruit).

5. Plants short, 3–20 (–25) cm tall, few-flowered (1–5 or rarely 7–10 flowers per stem axis); pedicels ascending; leaves narrowly triangular (tapering evenly from a base up to 2.3 mm broad), ± crowded and strongly ascending.

S. longipes

5. Plants taller, few- to many-flowered; pedicels and branches of inflorescence (at least when mature) strongly divaricate or reflexed; leaves linear to narrowly lanceolate, ± spreading.

6. Median (if not all) leaves broadest at or just above the base; margins of leaves and stems not papillose (rarely ciliate); bracts and usually sepals ciliate; seeds distinctly wrinkled with wavy sculpturing.

S. graminea

6. Median (if not all) leaves linear or slightly broader near the middle; margins of at least upper leaves and angles of the internodes between them finely papillose [20×]; bracts and sepals usually not ciliate; seeds slightly marbled but essentially smooth.

S. longifolia

All species found in Stellaria

Stellaria borealisNORTHERN STITCHWORT 
Stellaria crassifoliaFLESHY STITCHWORT 
Stellaria gramineaSTARWORT 
Stellaria longifoliaLONG-LEAVED CHICKWEED 
Stellaria longipesSTARWORT 
Stellaria mediaCOMMON CHICKWEED 
Stellaria pallidaLEAST CHICKWEED 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. December 11, 2017. http://www.michiganflora.net/genus.aspx?id=Stellaria.