This is a Devil Tree.

The Devil Trees are powerful and malign beyond human comprehension. They come from the seeds Adam spat out from the apple, or from the stakes in the hearts of vampires, or from a rotten root of the world-tree Yggdrasil, depending on who you ask. They arise in lonely unhallowed places, where they are approached by shadowy supplicants who make unspeakable wishes and offer obscene sacrifice.

But not this one, which has arisen by cthonic error in the garden of Oliver Teabucket. It would have made a bloody wreck of Mr Teabucket if he had tried to remove it, but Mr Teabucket thought it striking enough to leave in place: it set off the bright hues of the Cherry Blancmange roses. Now it stands hunched in on itself among the pastels and primary colors of Mr Teabucket's flowers. At intervals a shadowy supplicant will creep up the garden path, pause, look round, and slink away in searing embarrassment.

But today Mr Teabucket himself approaches, bearing an object. The Tree feels a stir of dark hope - has its presence sown corruption in the fool's soul and caused him to at last make obeisance? The man comes closer, and hope turns to cankerous horror. For in Mr Teabucket's hands is a gnome. Its hat a fluorescent red-and green, face set forever in a cheery grin and an unending wink, torso in a T-shirt bearing the message "I Really Dig Gardens". This offering Mr Teabucket places at the roots of the Devil Tree. And the Devil Tree screams rage and anguish across a thousand dimensions, but Teabucket hears it not.

(Shamelessly inspired by Katy Towell's Halloween poem "Bone Trees". I can't find a link to that now, unfortunately. :( )