Its one of the gymnangosporium rusts, a fungal infection - these protrusions mean its 'hatching out' and now will be seeking either a pear or apple tree in order to complete its life cycle. People usually worry more about their apples and pears than they do the conifer (usually juniper) that's hosting the first part of the fungal life cycle - there is no treatment. At an earlier stage, before these 'horns' appear, you can cut out any growths you see, but if you've an apple or pear tree, I'd get rid of this plant.

Wow Bamboo, how interesting! Only of course if it's not in your own garden! All a bit like an alien invasion, never seen this before which just goes to prove we all learn something new every day - fascinating.
Sorry about your tree though Richard.

Sadly, these infections are becoming much more widespread, so you'll probably encounter it at some point, Honeysuckle, maybe in a park or a neighbour's garden.

Many thanks Bamboo---Unfortunately I have both apples and pear trees in the garden, lets hope I`m not too late !!!