These are strikingly large plants, with big heads and usually very large leaves. Both surfaces of the leaves (or chiefly the upper in S. integrifolium) are strongly roughened with small, pale, hard papillae, these sometimes with a tiny sharp tip.

Sliphium are quintessential prairie plants and are commonly used in plantings throughout the state, despite the fact that all but S. terebinthinaceum occurred naturally only in very small portions of southernmost Michigan. Three of our species, S. integrifolium, S. laciniatum, and S. terebinthinaceum, may occur along railways, sometimes with other prairie plants in depauperate remnants. As these occurrences are widely dispersed, well beyond areas from which the oldest collections are known, it is likely that these outlier populations are recent disperals, rather than persisting from native populations.

1. Principal leaves all opposite (occasionally whorled).

2. Leaf bases sessile (or even slightly clasping) but not connate, on a ± terete stem.

S. integrifolium

2. Leaf bases connate around a strongly 4-angled stem.

S. perfoliatum

1. Principal leaves alternate or basal.

3. Leaves alternate, deeply pinnately lobed.

S. laciniatum

3. Leaves basal, unlobed (occasionally one or more much-reduced cauline leaves present).

S. terebinthinaceum