This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
It is unnecessary to go into the details of the technical characters of this familiar genus, farther than to enable the beginner to distinguish it from Bulbocddium and Colchicum, two genera very similar in habit though belonging to a different family with 6 stamens and a free ovary. The bulbs or corms are more or less densely clothed with fibrous coats. Leaves all radical, linear, enveloped in a scarious sheath at the base. Flowers solitary or fascicled,almost sessile on the bulb. Perianth - tube long and very narrow. Stamens on the bases of the outer segments. Ovary underground. Stigmas more or less cleft or fringed. Confined to the northern hemisphere in the Old World and particularly abundant in Asia Minor and the Mediterranean region. The old Greek name. The species and varieties in cultivation are exceedingly numerous and difficult of discrimination. We can only afford space for short descriptions of the commoner species.1 For convenience we may divide them into vernal and autumnal species. The former alone are very generally cultivated, as they appear at a season when other flowers are scarce.
1 Chiefly taken from an outline key, kindly communicated by Mr. J. G. Baker.
Fig. 232. Crocus vermis. (1/2 nut. size.)
§ 1. Flowers vernal. Stigmas not multifid.
1. C. vernus (fig. 232). - This is the species principally cultivated and the parent of numerous varieties both of garden and wild origin. Leaves dark green with a central longitudinal white stripe. The purple, violet, white and striped varieties of these colours belong to this species. The hairy throat of the perianth is the most reliable character. Widely distributed in Europe.
2. C. reticulatus, including C. Susianus. - Bulb-coats in this and the next species with very strong prominent fibres. Perianth naked at the throat; flowers yellow, distinguished from other yellow-flowered species by the brown colour of the exterior of the perianth-tube. South of Europe.
3. C. variegatus. - Very like the last, but the flowers are purple. Asia Minor.
4. C. luteus. - Bulb-coats with finer fibres; flowers yellow. To this are allied C. aureus, C. lagenafldrus, C. stellaris, and several other forms. South Europe and Asia Minor.
5. C. bifldrus. - Flowers white or striped externally with purple, yellow within. C. versicolor is referred to this. Crimea.
6. C. Imperati. - Similar to the last. Flowers lilac striped with purple. One of the earliest blooming species. Italy.
§ 2. Flowers autumnal. Stigmas not multifid.
7. C. sativus. Saffron Crocus. - This is the most familiar of the autumn-flowering Crocuses. Leaves not fully developed at the time of flowering. Flowers violet, variously striped, and marked with deeper or lighter tints. Perianth-tube hairy. Frequently seen in different countries in a naturalized state, but its native country is not known with certainty.
§ 3. Floivers autumnal. Stigmas multifid. Leaves not appearing at the same time as the flowers.
8. C. speclosus - A beautiful large-flowered species. Flowers purple or blue, feathered with different tints. Stigmas yellow, conspicuously fringed. This includes C. pulchellus. Southwestern Europe.
9. C. nudiflorus. - Flowers of a uniform purple or violet. Perianth not hairy at the throat. This species is found in some parts of England, but is probably not indigenous. It flowers in October or November.
There are very many other species, some of which are occasionally seen in Botanic gardens, but the above include all the commonly cultivated forms.