Hepaticas
Plants of the buttercup family, with anemone-like flowers, native to north temperate regions.
Ridge
A long narrow hilltop, mountain range, or watershed.
Wide-spread
Spread widely. Also: general, extensive, ubiquitous, or sweeping.
Cornel-root
A term used by the speaker to describe the root of a cornel flower, which is a casual nickname for several possible flowers. In this poem, given that the cornel-buds are white, the speaker may be referring to a flower of the dogwood family.
Leaf-shadow
The shadow cast by a leaf at dusk, as the light becomes low in the sky.
