Lithospermum

1. Corolla ± cylindrical, the lobes acute, barely if at all spreading; anthers ca. 1.5–3.5 mm long.

L. molle

1. Corolla funnelform or salverform, the lobes (especially if corolla over 10 mm long) usually spreading, not pointed; anthers 0.3–2 mm long.

2. Corollas light to deep yellow, showy, the limb 9–22 (–25) mm broad, much exceeding the calyx; plants with a terminal inflorescence (inflorescence elongates later in season and flowers may then appear ± axillary).

3. Corolla with tube (unexpanded portion) 22–35 mm long and lobes distinctly erose or fringed; leaves narrowly linear, mostly less than 4 mm wide (a few as wide as 6.5 mm); pubescence on stem entirely of closely appressed hairs.

L. incisum

3. Corolla with tube 6–14 mm long and lobes entire (though often undulate); leaves mostly broader; pubescence, at least on stem, all or partly spreading.

4. Calyx lobes 2.2–4.5 (–5) mm long (to 6.5 mm in fruit); pubescence of leaves, stems, and bracts soft, usually not pustulate-based.

L. canescens

4. Calyx lobes (5–) 6–10 (–13) mm long; pubescence largely of very stiff slightly pustulate-based hairs.

L. caroliniense

2. Corolla white to pale yellow or greenish, the limb less than 8 mm broad, barely if at all exceeding the calyx (at most by 1.5–2 (–3) mm); plants with flowers appearing mostly axillary.

5. Largest leaves or bracts 2–4 cm broad; cauline leaves usually 15–20 or even fewer below the inflorescence; pubescence of leaves and stems all or mostly closely appressed.

L. latifolium

5. Largest leaves or bracts (0.5–) 0.7–2 cm broad; cauline leaves at least 25–30 below the inflorescence; pubescence, especially on undersides of leaves, mostly somewhat ascending (raised, not appressed).

L. officinale

All species found in Lithospermum

Lithospermum canescensHOARY PUCCOON 
Lithospermum carolinienseHAIRY PUCCOON, YELLOW PUCCOON, PLAINS PUCCOON 
Lithospermum incisumFRINGED PUCCOON 
Lithospermum latifoliumAMERICAN GROMWELL, BROAD-LEAVED PUCCOON 
Lithospermum molleMARBLEWEED, FALSE GROMWELL 
Lithospermum officinaleGROMWELL 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. March 27, 2017. http://michiganflora.net/genus.aspx?id=Lithospermum.