Retinispora
Read about Retinispora in the Standard Cyclopedia of Horticulture
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Retinispora. Often but not originally spelled Retinospora. A genus of conifers founded originally by Siebold and Zuccarini on the two Japanese species of Chamaecyparis, chiefly distinguished from the American species by the resinous canals of the seeds (from Greek, retine, resin, and spora, seed). Afterward the genus was united with Chamaecyparis, but in horticultural nomenclature the name is applied to a number of juvenile forms of Thuja and Chamaecyparis, chiefly those introduced from Japan. As these juvenile forms all resemble each other very much, indeed much more than do the typical forms to which they belong, it is not strange that they should have been considered to be distinct species and even to belong to a separate genus. Even botanists failed to recognize the true relation of these forms and went so far as to place one of them in the genus Juniperus. With the exception of Retinispora ericoides, which C. Koch recognized as the juvenile form of Thuja occidentalis, the origin of these juvenile forms remained doubtful until L. Beissner, after having carefully studied the subject for years, disclosed the relationship of the various forms. He showed by experiment that it is possible to raise the same form by making cuttings from seedlings which have still retained their primordial foliage, and he also published cases in which larger plants of these doubtful forms have been observed accidentally to develop branches with the foliage of the typical form. See, also, Gt. 1879, pp. 109 and 172; 1881, pp. 210 and 299, and 1882, p. 152. There are four of these juvenile forms generally in cultivation, each of them with an intermediate form showing either a kind of foliage approaching that of the type or two different kinds of foliage on the same plant. There seems to be no doubt that all these forms have been secured by propagating branches of young seed- ling plants. All seedlings of Chamiaecyparis, Thuja, and other genera of the Cupressineae produce in their juvenile state a kind of primordial foliage very different in appearance from that of the adult plants. The first leaves are always linear and spreading, passing gradually into acicular and at last scale-like leaves. In some plants, especially if they have not sufficient nourishment, the primordial foliage is retained longer than usual and these have probably been selected for perpetuating the juvenile state, by means of cuttings. By continuing through many generations the propagation of those branches which show the juvenile state most distinctly, these forms have become well-fixed varieties and even sometimes bear seeds without changing the foliage on the fruiting branches. These seeds, however, produce plants of the typical form and only a few of them retain the primordial foliage somewhat longer than usual. The juvenile forms very much resemble some species of Juniperus in habit and foliage. They bear linear spreading leaves in pairs, changing in winter to a brown, reddish, violet or steel color, and do not show the regular frond-like branching of the typical forms. The leaves, however, are much softer and not sharply and acutely pointed as in Juniperus; they are mostly marked with whitish or grayish green lines beneath, which is never the case in Juniperus. Only Thuya orientalis var. decussata and some intermediate forms, with acicular suberect leaves, show whitish marks on the upper side of the leaves like Juniperus. Though these Retinispora forms are described under the genera and species to which they belong, where also references to illustrations are cited, descriptions are given here to afford a closer comparison of these similar and much confounded forms. The two forms of foliage in the common red cedar are well shown in Fig. 2025, Vol. III. For other pictures of Retinispora forms see Chamaecyparis and Thuja. Chamaecyparis obtusa var. ericoides, Boehmer (Retinispora Sanderi, Sander. Juniperus Sanderi, Hort.). Dense round-headed bush with upright branches and bluish gray foliage: lvs. acicular, decussate, spreading, about 1/5in. long, thickish, concave above and with a green line in the middle, the lower lvs. often acutish, the upper ones obtuse. Chamaecyparis pisifera var. squarrosa, Beissn. & Hochst. (Retinispora squarrosa, Sieb. & Zucc.). Fig. 893. A dense, pyramidal or round-headed bush or sometimes small tree, with light bluish green foliage almost silvery white when young, usually coloring violet in winter: tips of branchlets nodding: lvs. crowded, spreading, very soft, bluish green above, silvery white below. Tne most ornamental and graceful and the best known of these juvenile forms. The intermediate form, var. plumosa, Beissn. & Hochst. (Retinispora plumosa), has smaller, subulate and suberect lvs., and is much planted, especially in its golden variegated form. See Fig. 892, Vol. II. Chamaecyparis thyoides var. ericoides, Sudw. (Retinispora ericoides, Zucc.). Fig. 3369. Dense shrub, of stiff, pyramidal or almost columnar habit, with upright branches and bright green foliage, changing to violet-red or brownish red in winter: lvs. bright green above, with 2 bluish lines below. This form is very distinct with its stiff, columnar habit, but is less common in cult. The intermediate form, var. andelyensis, Schneid. (Retinispora leptoclada, Hort.), shows also a stiff, pyramidal habit ana bears chiefly small, suberect or almost scale-like lvs., and occasionally branchlets with spreading linear lvs. Fig. 3369. Thuja occidentalis var. ericoides, Beissn. & Hochst. (Retinispora ericoides, Hort. R. dubia, Carr.). Dense broadly pyramidal or round-headed bush, with upright branches and dull green foliage, changing to brownish green in winter: lvs. linear, soft grayish green beneath. The intermediate form, var. Ellwangeriana, Beissn. (Retinispora Ellwangeriana, Hort.), has usually two kinds of lvs., but the linear lvs. are smaller than those of the preceding form. Thuja orientalis var. decussata, Beissn. & Hochst. (Retinispora juniperoides, Carr. R. decussata, Hort. R. squarrosa, Hort.). Fig. 3369. Dense, round-headed bush, with bluish green foliage changing to violet or steel-color in winter: lvs. rather rigid, bluish green, spreading, concave and with a whitish line above. But rarely cult, and not quite hardy N. The intermediate form, var. meldensis, Laws. (Retinispora meldensis, Hort.), has mostly acicular suberect lvs. of the same color as in the preceding var. andelyensis. These juvenile forms are valuable for formal gardening, for rockeries, small gardens and wherever slow- growing and dwarf conifers are desired. They are short-lived and usually becomes unsightly when older. They are all readily prop, by cuttings. See also Chamaecyparis and Thuya.
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Read about Retinispora in the Standard Cyclopedia of Horticulture
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References
- Standard Cyclopedia of Horticulture, by L. H. Bailey, MacMillan Co., 1963
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