Acicular

Near-synonyms: needlelike, pinlike

1992, Oliver Sacks, Migraine, Berkeley: University of California Press, revised and expanded edition, Part 5, Chapter 17, p. 279, Sometimes these networks have an acicular or crystalline appearance, and may grow visibly, sometimes with sudden jerks, “like frost on a windowpane,” or “primitive plants.”

the acicular foliage of coniferous trees

[…] though fond of foliage, their trees always had a tendency to congeal into little acicular thorn-hedges, and never tossed free.