This section is from the book "The Gardener V3", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
Saxifragas, in the mossy and silvery-leaved sections, present a rather numerous list to select from. The effect of both in winter is beautiful, especially in gardens where gravel and stone-work abound. Some of the mossy section are peculiarly bright in winter, when they are managed so as to prevent their becoming patchy. They should be planted every year in order to keep them compact and smooth; and at any time during the growing season they may be attended to in the matter of making good weak spots, so that a fine even surface may be constantly maintained. S. aizooa is one of the silvery or incrusted-leaved class. The leaves are short, blunt, and arranged in rosettes, which, like most of this class, are liable to become tufted and uneven if they are not annually divided and replanted. S. caespitosa belongs to the mossy section, is more disposed to become tufted in the course of a year's growth than some others, and therefore requires a little attention in order to keep it smooth. A little pressure with the hand or foot, applied occasionally to the centre of the tufts when they begin to assume a tendency to become uneven, will put all right. S. crustata belongs, as the name implies, to the incrusted group, and is similar in character to the first named, and requires similar treatment.
S. hypnoides belongs to the mossy section: it is less inclined to become tufted than ccespitosa, but will require some attention in that respect in order to keep it neat and dressy. It is, perhaps, the best of the mossy section for the purpose in view, being compact in habit, and of a very pleasing lively colour. Similar to, and indeed closely resembling it, are the sorts grown under the names affinis, decipiens, hirta, incurvifolia, and others which, by botanists, are regarded as only slight variations from the typical form of the species. S. ligulata belongs to the incrusted group. The leaves are narrow, and form very neat and pretty rosettes, assuming a very bright silvery tint. It is, in fact, a miniature of the next species, and only suitable for margining small beds and clothing small circles with a silvery mass, in the centre of which some contrast in colour and habit may be put. S. longifolia is one of the handsomest of the section with crusted leaves. It has been called the queen of Saxifragas. Others might dispute its title as applying collectively to the genus, but it is indisputably the queen of the section to which it belongs. When well cultivated, this beautiful plant forms leaves of considerable length, and rosettes of perfect symmetry, seven or eight inches across.
Left to itself, it is apt to become tufted and rough, but if divided and replanted annually, it forms one of the most attractive carpeting plants imaginable. S. cotyledon, another of the incrusted species, better known in one of its forms as pyramidalis, is larger leaved, and forms larger and bolder rosettes. It requires the same attention in regard to annual dividing and replanting as the others of this section. There are a few other incrusted species and varieties which may be used - any of the section being adaptable to different purposes and positions in the way contemplated - but it is quite needless to describe them. They all require similar treatment.