A. graveolens: stems rather slender, branched, furrowed, glabrous, 1-2 feet high; leaves pinnate, with 3-5 broad cre-nate or three-lobed segments; umbels small, nearly sessile on the upper branches opposite the leaves, or on very short terminal peduncles, of 3-6 rays, bearing numerous small white flowers on short pedicels; fruits very small. - Marshy places near the sea. Fl. June to August. The Celery of our gardens is a cultivated variety, with enlarged leafstalks.
H. nodiflorum: stems procumbent, rooting, the flowering ones ascending or nearly erect, 1-2 feet high, glabrous; leaves pinnate, with 3-10 or more pairs of ovate-lanceolate toothed segments; umbels nearly sessile, either opposite to the leaves or between the upper branches, with 5-6 (rarely 8 or 4) rays; general involucre usually wanting; partial involucre of several small, lanceolate bracts. - Marshy meadows and ditches. Fl. July, August. It varies much in size and foliage.
H. repens is a smaller, much branched, more creeping form, with 3-5 small broad leaf-segments, and longer peduncles to the umbels, occasioned by growing in drier situations.
H. inundatum: stems glabrous, creeping and rooting at the base like H. nodiflorum, but smaller, and more slender, often partly immersed in water, the submerged leaves divided into capillary segments; flowering stems 6-8 inches high, with small ternate or pinnate leaves, the segments three-toothed or three-lobed, each lobe often again three-toothed; umbels on short peduncles opposite the leaves, generally of 2-3 rays without involucre, the partial umbels of 5-6 small flowers, with 2-3 minute bracts. - Swamps and shallow pools. Fl. June, July.