This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
(classical name, of no significance to these plants). Gentianaceae. Herbs treated either as annuals or biennials or perennials, with flowers of white, lilac, blue or dark purplish blue, cultivated in a very few greenhouses.
Very rarely suffruticose: dwarf or tall and paniculate-branching: leaves sessile, clasping or short-stalked, ovate or lanceolate, mostly 3-5-nerved: flowers small or attaining 2 in. across, rotate, pedicelled or not, in forking cymes; calyx 4-5-parted, the segments keeled, winged or flat and 3-nerved; corolla-lobes 4 or 5, ovate or oblong, twisted; stamens 4 or 5, attached to the throat, with very short filaments, the anthers opening by apical pores that finally enlarge nearly to the base: fruit a globose 2-valved caps. - Species about 30, in tropical and Subtrop. Asia, Malaysia, tropical Africa, Socotra.
Plants of E. affine flower in summer. If specimens in 5-inch pots are desired, sow in March of the same year; for larger specimens, sow in August of the preceding year. The plants must be kept in a cool but not draughty greenhouse or frame in summer, and shaded from fierce sunlight. They usually are given warmhouse conditions.
a. Leaves with stalks often 1/2in. long.
Balf. stem cylindrical, 1-2 ft. high, much branched from the base: leaves 1-1 1/2 in. long, elhptic-ovate, faintly 3-5-nerved: sepals with a broad wing on the back; corolla 6-9 fines wide; lobes almost rounded. Socotra. B.M. 6824. A.F. 13:1104. Gng. 6:229. R.H. 1883, p. 512. Gt. 32:1108. G.C. II. 21:605.
aa. Leaves nearly or quite stalkless.
B. Corolla-lobes rounded.
Roxbg. Annual: stem 4-sided, branched only above: leaves becoming 3 in. long, strongly 3-nerved, elliptic-oblong, acuminate, narrower than in E. affine, and tapering: flowers blue, 1 1/2 in. across, in terminal, leafy corymbs; sepals broadly winged; corolla-lobes obovate, obtuse. Ceylon. B.M. 4423 (sky-blue, with a dash of purple). R.H. 1859, p. 238. J.F. 1:43. H.F. II. 2:60.
bb. Corolla-lobes usually tapering to a point.
Am. (E. zeylanicum variety macranthum). Fig. 1468. stem cylindrical, slightly branched: leaves as in E. zeylanicum, though perhaps more variable from base to summit: flowers purplish blue, 2 in. across. In both species there is a narrow ring of yellow at the mouth, to which the conspicuous clusters of stamens are attached. Ceylon. B.M. 4771 (deep purplish blue). G.C. III. 15:331. R.H. 1911, p. 31. J.H. III. 42:182; 51:259. - The best of the genus. The rich, dark blue is worth striving for.
Fig. 1468. Exacum macranthum ( X 1/3).
Forbesii, Balf. Bushy and shrubby: leaves triangular or ovate-lanceolate, 1 1/4 in. across at base: flowers upwards of 1/2in. across, purple or violet-purple, in terminal racemes, the anthers yellow and prominent. Socotra. G.C. III. 31:93. G. 23:679. G.W. 6, p. 290. G.M. 45:81. - A good plant for intermediate temperature, blooming well in a 6-in. pot. Wilhelm Miller.
L. H. B.†