What is "thorn broom"

Thorn \Thorn\, n. [AS. [thorn]orn; akin to OS. & OFries. thorn, D. doorn, G. dorn, Dan. torn, Sw. t["o]rne, Icel. [thorn]orn, Goth. [thorn]a['u]rnus; cf. Pol. tarn, Russ. tern' the blackthorn, ternie thorns, Skr. t[.r][.n]a grass, blade of grass. [root]53.]

1. A hard and sharp-pointed projection from a woody stem; usually, a branch so transformed; a spine.

2. (Bot.) Any shrub or small tree which bears thorns; especially, any species of the genus Crat[ae]gus, as the hawthorn, whitethorn, cockspur thorn.

3. Fig.: That which pricks or annoys as a thorn; anything troublesome; trouble; care.

   There was given to me a thorn in the flesh, the messenger of Satan to buffet me.
   --2 Cor. xii. 7.

   The guilt of empire, all its thorns and cares, Be only mine.
   --Southern.

4. The name of the Anglo-Saxon letter ?, capital form ?. It was used to represent both of the sounds of English th, as in thin, then. So called because it was the initial letter of thorn, a spine.

   Thorn apple (Bot.), Jamestown weed.

   Thorn broom (Bot.), a shrub that produces thorns.

   Thorn hedge, a hedge of thorn-bearing trees or bushes.

   Thorn devil. (Zo["o]l.) See Moloch, 2.

   Thorn hopper (Zo["o]l.), a tree hopper ( Thelia crat[ae]gi) which lives on the thorn bush, apple tree, and allied trees.