in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 5: 692. 1836.
Leaf-blades 50–175+ × 2–8 (–12+) mm. Involucres hemispheric to ± urceolate or globose, 3.5–12 × 3–8+ mm. Ray laminae 5–12 mm. Disc corollas 2.5–3.5 mm. Cypselae black, 2–3.5 mm.
Subspecies 6 (6 in the flora).
|1||Heads in spiciform-racemiform to spiciform-paniculiform arrays (heads ± sessile); ray laminae white, abaxially purple-veined||> 2|
|1||Heads in racemiform or paniculiform arrays or in glomerules; ray laminae white or yellow, abaxially purple-veined or not||> 3|
|2||Peduncular bracts not or barely surpassing phyllaries; calyculi 0; phyllaries 3–7 mm, apices usually shorter than bodies; cypsela widths 0.6–0.75 times lengths||Hemizonia congesta subsp. clevelandii|
|2||Peduncular bracts (and calyculi) often notably surpassing phyllaries; calyculi usually of 5–7, sometimes 0, bractlets; phyllaries 6–12 mm, apices usually longer than bodies; cypsela widths 0.5–0.6 times lengths||Hemizonia congesta subsp. calyculata|
|3||Leaves usually puberulent and eglandular throughout, rarely the distal villous and glandular; heads in paniculiform arrays; ray laminae white, not purple-veined||Hemizonia congesta subsp. tracyi|
|3||Leaves pubescent, sericeous, or villous, all or the distal glandular; heads in paniculiform arrays or in glomerules; ray laminae white or yellow, abaxially purple-veined||> 4|
|4||Leaves ± villous (the distal with hairs at margins often longer); some or all heads usually in glomerules, sometimes in corymbiform or paniculiform arrays; phyllaries 6–10 mm, apices usually longer than bodies; ray laminae white||Hemizonia congesta subsp. congesta|
|4||Leaves pubescent, villous, or sericeous (the distal with hairs at margins not notably longer); heads in paniculiform arrays; phyllaries 3–7(–8) mm, apices usually shorter than bodies; ray laminae white or yellow||> 5|
|5||Ray laminae white||Hemizonia congesta subsp. luzulifolia|
|5||Ray laminae yellow||Hemizonia congesta subsp. lutescens|