Common and Midland Hawthorn, and Blackthorn are our native thorns and all of them flower, but I suppose any prickly bush could be referred to as a thorn.

This stanza isn't in the earliest version

just 2 stanzas form her task.

For thou must shape a sark to me
Without any cut or hem, quoth he.

Thou must shape it needle and sheerless
And also sew it needle threedless