Onion

Aggregate onion (var. aggregatum): bulbs clustered and no scape developed, the plants propagated by bulbs; by contrast common onion (var. cepa) has a solitary bulb, a developed scape and umbels without bulblets.

Tree onion (var. proliferum): a variety whose umbel carries bulblets along with a few flowers; the perianth is white with pale red midveins.

The bulb is solitary or clustered, flattened-globose to ovoid, with papery purple-red, brown-red or yellow tunics; leaves are terete and hollow; the scape reaches 1 m, inflated below the middle, bearing a dense globose umbel of chalk-white or greenish-white flowers.