holly
柊 refers specifically to the holly plant, a spiny-leaved evergreen often associated with winter.
柊 combines 木 (tree) with 冬 (winter), likely indicating a tree associated with winter, fitting the holly's evergreen nature and winter berries.
A tree 木 that stays green through winter 冬: that's the holly 柊, with its spiky leaves and red berries.
For シュ, imagine a shoe hanging from a holly branch: shoe -> シュ, and the prickly leaves keep it in place.
holly olive (Osmanthus heterophyllus); false holly
Mahonia japonica; Japanese mahonia
mizuna (Brassica rapa var. nipposinica)
sardine and holly charm; sardine head and holly branch placed next to the front door during setsubun to ward off demons
English holly (Ilex aquifolium)