Not too many shrubs listed with the starting letter of X but we will work on this section and find some more.
We are helped out by the fact that many plants have an x as a prefix to their name proper. The x denotes that the plants are inter-generic hybrids! As such they are normally infertile.
x Fatshedera lizei has clues in it's specific name as to its two parents from same genera - but different species! Both are from the Genera Araliaceae. The Fatsia japonica and the Hedera. It is an interesting cross, for both parents have palmate foliage. But now we have a bi-generic hybrid having distinct qualities from both parents. It is probably mistaken for a Hedera (Ivy) rather than a Fatsia (False Aralia or Japanese Aralia), for whilst it has a rather floppy upright habit of growth, it has leaves which are nearer in size to the large leaved Ivies, and not as big as the large palmate leaves of the Fatsia.
It is more often used as a Fatshedera lizei houseplant, but is reasonably hardy enough to be classed as a shrub. And it does so much to help me fill this page of shrubs starting with letter X (Please forgive!) It is commonly known as the Tree Ivy and has a nicely variegated form as well as the normal green foliage type.
Xanthoceras: - Very hardy - yet sheltered position best - very attractive, yet rarely grown. Erect white flower stems. Deciduous and late to show growth in the spring, may lead you to believe that it has died.
Xanthorhiza A single species plant with a suckering habit - though nonetheless attractive for that provided it is allowed space to develop. Commonly known as yellow-root, its new foliage is bronze - sometimes very brightly so - but then develops into green foliage. Flowers in nearly spring along with the bronze red foliage so quite attractive. Rarely grows more tat 60cm tall, but spread well because of its suckers.
x Fatshedera lizei Can be grown as a shrub, but needs to be protected for the fist winter. Thereafter best grown in a sheltered spot. The variegated form - see image - is not as hardy as the basic green plant.
x Halimiocistus cultivars - These are popularly known as Cistus, but the C page is well filled thank you. The correct name of this inter-generic hybrid group in x Halimiocistus. Small growing evergreen shrubs well suited for the front of border; stone containers and of course rock gardens.
x Sinocalycalycanthus raulstonii as its name suggests, the parentage included a Calycanthus, and is similar in many respects to the Calycanthus. Like its parent, it is fully hardy and is at home in full sun or dappled shade.
Xylosma japonica - of which I know nothing!
Xanthoxylum Is now generally known and written as Zanthoxylum on account of that is the way it is pronounced. As with Xylophone, the X conveniently becomes Z.