Euphorbia

Mediterranean spurge (Euphorbia characias) is an architectural evergreen sub-shrub of the Mediterranean Basin, forming an upright dome of blue-green, closely set, strappy leaves to about 4 feet. From late winter through spring it is topped by big, dense, dome-shaped heads of chartreuse-green flower structures (cyathia) that hold their acid-lime colour for months and give the plant a sculptural, almost otherworldly presence. It is tough, drought- and salt-tolerant, and evergreen year round, but it comes with a real safety flag: like all spurges it bleeds a milky white latex when cut or broken, and that sap is a skin and eye irritant. Handle it with gloves and eye protection, and keep the cut sap away from skin and face.

The world's most famous holiday plant is, in its homeland, a leggy tropical shrub. Native from Mexico to Guatemala, Euphorbia pulcherrima is grown almost everywhere as a compact potted gift for its blaze of winter color - but that color is not flowers. The showy red, pink, white, or marbled 'petals' are bracts (modified leaves); the true flowers are the small yellow-green cup-like cyathia clustered at the center. The bracts color up only in response to long, uninterrupted nights, which is why poinsettias turn for the winter holidays and why a houseplant in a lamp-lit room often refuses to re-color. It is frost-tender and hardy in the ground only in USDA zones 9a-11b, where it grows into an open, erect, multi-stemmed shrub 3-12 feet tall. A persistent caution: it is MILDLY toxic - the milky white latex (sap) can irritate skin and eyes and cause mild stomach upset if eaten - but its deadly reputation is a long-debunked myth, not a real hazard.