Osha can be confused with many plant species in the parsley family. It has been confused with the toxic
poison hemlock (
Conium maculatum) and
water hemlock (
Cicuta). Other plants misidentified as osha include
hemlock parsley (
Conioselinum), mountain parsley (
Pseudocymopterus montanus), species in genus
Ligusticum, and
biscuitroots (
Lomatium) especially when young. Osha particularly resembles poison hemlock, but is easily distinguished from it by its "spicy celery" odor, hair-like material on root crowns, and dark chocolate-brown, wrinkled root skin. Hemlock roots are white and fleshy and thin-skinned; they are typically heavily branched rather than carrot-like, but this is not always the case. Poison hemlock roots have little or no odor; the plants themselves smell "musty" or "mousy", or rank. Osha leaves have an intense fragrance when bruised and are typically larger than those of poison hemlock. Most poison hemlock plants have purple blotches or shading on the lower stem if they are fairly mature, but again, this is not always the case. Unlike its poisonous cousins, osha does not tolerate overly moist soils (because it depends on mycorrhizal fungi) and is never found growing in standing water. Nevertheless, osha and poison hemlock can be found only a few feet from each other. If the plant is growing near water in consistently moist soil, is tall (0.75–2m), has purple splotches on the main stem, and is heavily branched with small umbels of white flowers, it is probably poison hemlock and should be avoided. In any case, due to the high toxicity of poison hemlock, if a supposed osha plant cannot be positively identified, it must be discarded.
Coniine, the main poison in hemlock species, can be absorbed through the skin. People who have come into contact with these plants, including crushing the leaves to perform a "smell test," should wash their hands immediately and avoid touching their eyes or mouth.
Cow parsnip (
Heracleum lanatum,
Heracleum maximum, Indian celery, or pushki, sometimes considered a subspecies of
Heracleum sphondylium, hogweed or eltrot) is also confused with osha and other plants with similar flower groupings. However, cow parsnip has large, broad leaves and an unpleasant odor. == Cultural associations ==