WordNet sense 1 (a herbaceous plant of the genus Scutellaria which has a calyx that, when inverted, resembles a helmet with its visor raised):

skullcap

WordNet sense 2 (any of several orchids of the genus Coryanthes having racemes of a few musky-scented waxy flowers with a helmet-shaped lip process):

helmet orchid

WordNet sense 3 (a poisonous herb native to northern Europe having hooded blue-purple flowers; the dried leaves and roots yield aconite):

monkshood, Aconitum napellus