An important group of hybrids between F. suspensa and F. viridissima, of which the first to be observed and described arose shortly before 1885 in the Göttingen Botanic Garden, Germany. The same cross had been made deliberately by Meehan in America before 1868, but whether plants were raised from it is not known. They are shrubs 6 to 8 ft high with erect or arching stems; pith usually irregularly lamellate. Leaves ovate or lanceolate, toothed at least in the upper half, sometimes three-parted on vigorous shoots. Flowers borne in twos and threes from each leaf-scar but singly in some clones. Calyx more than half as long as the corolla-tube, or equalling it in some clones. Corolla-lobes 11⁄4 to 11⁄2 in. long, usually spreading and often revolute and twisted.
Numerous cultivars of F. × intermedia have been raised, and descriptions of the earliest of these will be found in the article by Koehne in Gartenflora, Vol. 55 (1906), pp. 226-230. The following are the best known, but of the old clones only ‘Spectabilis’ is common in commerce:
‘Arnold Giant’ and
‘Densiflora’. – Flowers crowded, light yellow, usually borne singly; calyx as long as corolla-tube. Corolla-lobes about 11⁄4 in. long, spreading, not markedly revolute. Long-styled. Raised by Späth and put into commerce 1899.
‘Karl Sax’. See under
‘Lynwood’. – A bud-sport of ‘Spectabilis’, which arose in the garden of Miss Adair of Cookstown, Co. Tyrone, and was put into commerce by the Slieve Donard Nursery Co. in 1935. Leaves less toothed than in ‘Spectabilis’. Flowers borne freely all along the branches. Corolla-lobes not so spreading, with the edges less recurved. Considered by many to be superior to the parent.
‘Primulina’. – Superseded by ‘Spring Glory’, q.v.
‘Spectabilis’. – A vigorous shrub ultimately 10 ft high and as much across. Leaves ovate-lanceolate, 3 to 41⁄2 in. long. Flowers bright, rich yellow, densely and profusely borne. Calyx slightly shorter than corolla-tube. Corolla-lobes usually four in number, as is normal in Forsythia, but sometimes five or six, 11⁄2 in. long, about 5⁄16 in. wide, widely spreading, margins recurved, tips twisted. Short-styled. This, the best known of the forsythias and deservedly one of the commonest and most loved of garden shrubs, was raised by Späth and put into commerce shortly before 1906.
‘Spring Glory’. – A very free-flowering variety with light brown wood attaining a height of about 6 ft. Flowers bright sulphur-yellow, about 11⁄2 in. wide; corolla-lobes spreading, slightly recurved. Calyx as long as corolla-tube. Short-styled. It is a sport of ‘Primulina’, raised in the USA (the parent, which it supersedes, was raised in the Arnold Arboretum and described in 1912).
‘Vitellina’. – Flowers about 11⁄2 in. wide, rather deep yellow, tending to be clustered at the base of the previous season’s growth; calyx almost as long as the corolla-tube; corolla-lobes not or scarcely revolute; long-styled. Of erect habit. Put into commerce by Späth in 1899.
Polyploid Derivatives of F. × intermedia. – In 1939 a colchicine-induced tetraploid was raised at the Arnold Arboretum from F. × intermedia ‘Spectabilis’ and received the name ‘Arnold Giant’. Being difficult to propagate and sparse-flowering, this forsythia has not been widely planted. But in 1944 it was back-crossed to F. × intermedia ‘Spectabilis’ by Professor Karl Sax of the Arnold Arboretum, and a number of seedlings were raised. One of these proved to be triploid, but others that have been examined are tetraploid. At least one tetraploid clone was distributed to the trade by the Arnold Arboretum under the name ‘Beatrix Farrand’, but it appears that this name properly belongs to a triploid which is now extinct. The forsythia introduced to Britain under the name ‘Beatrix Farrand’ came from the Gulf Stream Nurseries, Virginia, USA, and a plant of this provenance received an Award of Merit when shown from the Savill Gardens, Windsor Great Park, in 1961. This was believed to be the true ‘Beatrix Farrand’, but investigations by G. E. Marks and K. A. Beckett showed that it, and others from the same source, were in fact all tetraploid (Journ. R.H.S., Vol. 88 (1963), pp. 351-352; see further in Vol. 91 (1966), pp. 307-308). Thus, through no fault of commercial growers, the tetraploid plant grown as ‘Beatrix Farrand’ is wrongly named and at the moment lacks a name.
A plant received from a nursery under the name ‘Beatrix Farrand’ has the following characters: it is of very vigorous, erect habit, producing stems from the base that grow up to 8 ft high in a single season. Leaves dull bluish green, very coarsely triangular-toothed. Flowers soft yellow, more or less nodding, the lobes oblong, truncate, almost plane, 3⁄4 to 1 in. long, 3⁄8 in. or slightly more wide; throat deeper yellow than the lobes, striated. They are short-styled, but in some flowers the style reaches up to the base of the stamens and pushes them apart. Fruits borne abundantly, ovoid with a short beak, producing fertile seeds. It is quite handsome in flower, but the foliage is ugly and the habit gaunt.
Another of Professor Sax’s seedlings has been named ‘Karl Sax’, and was described in Arnoldia, Vol. 20 (1960), pp. 49-50. This is of bushier habit than the forsythia called ‘Beatrix Farrand’ and less tall-growing. The corollas are a shade darker yellow, and being held more or less horizontally they show their deep yellow throats, which enrich the colour of the flowers seen en masse. ‘Karl Sax’ is also tetraploid and bears fruits. Bot. Mag., n.s., t.652.