Crocus is a genus in the Iridaceae family that is widespread, found in Europe, North Africa and in Asia. There are about 90 species. The standard reference on the genus is Brian Mathew, The Crocus, but at least half a dozen taxa, including new species, have been described since its publication. Other reference books that are helpful with this genus are The Smaller Bulbs and The Random House Book of Bulbs. A classic Crocus reference book is A Handbook of Crocus & Colchicum for Gardeners, by E. A. Bowles. It was first published in 1924 and is now out of data taxonomically, but it's an entertaining read by a legendary Crocus-lover.
Crocus Species in the Garden was the topic of the week for the Pacific Bulb Society list in February 2003. This discussion was led by Tony Goode. Click on this link for his Introduction. His Crocus Pages web site has images of most taxa and some basic information about all. John Lonsdale also has an extensive Crocus collection, and has posted photos at his Edgewood Gardens website. Smaller versions of a number of John's photos are reproduced in this wiki, with his permission.
Some species bloom in the fall, before, with, or after leaf dehiscence, some in the winter, and some in the spring. Seasonality is relative on these pages, which means the bloom time varies depends on where the grower lives. Those that bloom in the fall need a warm summer dormancy. Those that bloom in the spring need a cold dormancy. Those that bloom in the winter seem to bloom in winter of Mediterranean climate which is rather mild with little to no frost. Since frost is the limiting factor, the following pages are separated into fall blooming, and spring blooming for simplicity.
Crocus species are susceptible to viral disease. This is usually visible in the flowers. This distortion may take the form of twisted petals, streaking (as in tulip fire), sometimes the flowers are depauperate and fail to open properly. The virus also reveals itself as light and dark blotching in the foliage which is most visible when the foliage first emerges. The first three pictures here from Tony Goode have been manipulated to exaggerate the streaking in flower and foliage to make it more apparent. (Massive hike in contrast levels does this.) The third picture shows ones with distorted petals. The vectors are aphids which find refuge especially on the backs of the leaves. See the Virus page for more information. The fourth photo below is of a plant with Cucumber Mosaic Virus (CMV) and the last is a photo of Crocus speciosus which is infected with CMV and Iris Severe Mosaic Virus. Photos 4-5 from Janos Agoston.
In general Crocus plants have very short stems; the seed pods only become visible at the end of the growing season, long after the flowers have vanished, when the stems elongate. Sometimes the seed pods remain at or below ground level. Seeds may be of the sweet sticky type attractive to ants and thus growing best when sown at 2 or 3 cm depth after washing. Each year a new corm grows on top of the old one, which then dies, often extra corms are also produced. Photographs by David Pilling show seed pods, seeds on a 10mm grid and corm development.
Photos of a few of the species are shown below.
More information and photos of species can be found by selecting the fall and spring blooming Crocus wiki pages listed below or by clicking on a specific species in the table below.
Fall Blooming crocus A-H - Fall Blooming crocus I-O - Fall Blooming crocus P-Z - Spring Blooming crocus A-B - Spring Blooming crocus C-E - Spring Blooming crocus F-L - Spring Blooming crocus M-S - Spring Blooming crocus T-Z