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Crocus (; plural: crocuses or croci) is a genus of seasonal in the family Iridaceae (iris family) comprising about 100 species of perennial plant growing from . They are low growing plants, whose flower stems remain underground, that bear relatively large white, yellow, orange or purple flowers and then become dormant after flowering. Many are cultivated for their flowers, appearing in autumn, winter, or spring. The flowers close at night and in overcast weather conditions. The crocus has been known throughout recorded history, mainly as the source of saffron. Saffron is obtained from the dried stigma of Crocus sativus, an autumn-blooming species. It is valued as a spice and , and is one of the most expensive spices in the world. Iran is the center of saffron production. Crocuses are native plant to woodland, scrub, and meadows from sea level to alpine tundra from the Mediterranean, through North Africa, central and southern Europe, the islands of the Aegean Islands, the Middle East and across Central Asia to Xinjiang in western China. Crocuses may be propagated from seed or from daughter cormels formed on the corm, that eventually produce mature plants. They arrived in Europe from Turkey in the 16th century and became valued as an Ornamental plant flowering plant.
Crocus is an acaulescent (lacking a visible lower stem above ground) diminutive seasonal cormous (growing from ) Perennial plant geophytic genus. The corms are symmetrical and globose or oblate (round in shape with flatted tops and bottoms), and are covered with tunic leaves that are fibrous, membranous or coriaceous (leathery). The corms produce fibrous , and contractile roots which adjust the corms depth in the soil, which may be pulled as deep as into the soil. The roots appear randomly from the lower part of the corm, but in a few species, from a basal ridge.
The showy, salver to cup-shaped, single or clustered actinomorphic flowers taper off into a narrow tube; the flowers emerge from the ground, and can be white, yellow, lilac to dark purple, or Variegation in . The flower tube is long, cylindrical and slender, expanding apically. The floral tube is long and narrow with 6 lobes in 2 whorls. The perianth is 3+3 (3 sepals+3petals) and gamophyllous (with fused segments). The tepal whorls are similar, equal or subequal with a smaller inner whorl, and cupped to outspread. The bracts are membranous, but the inner ones are sometimes lacking.
The 3 are erect and linear and inserted in the throat of the perianth tube, with anthers shorter than the filaments. Pollen grains are inaperturate (apertures absent) but sometimes spiraperturate (spiral shaped). Each flower has a single style which is exserted (projecting beyond the corolla tube) and slender distally with three to many branches. The branches are highly variable, being short or long, and simple, bifurcate (dividing in two) or multifid and sometimes distally flattened. The inferior ovary has 3 carpels with axile placentation. It remains underground, and as the ripen, the pedicel (stem of the flower) grows longer so the fruit is above the soil surface.
While the flowers may vary dramatically between species, there is little variation in the leaves, but sufficient variability in corm tunics that they may be used as an aid in differentiating taxa.
The genus Crocus was first formally described by Carl Linnaeus in 1753, with three taxa, and two species, Crocus sativus (type species), var. officinalis (now treated as a synonym of C. sativus) and var. vernus (now Crocus vernus) and C. bulbocodium (now Romulea bulbocodium). Thus Linnaeus recognised two taxa that are accepted as separate species in modern classifications, one vernal and one autumnal crocus, but incorrectly assumed they were only varieties of a single species, while his second species was actually from a closely related genus that was only recognised later (1772). However, a subsequent re-examination of Linnaeus's specimens suggested the presence of several different species that he did not recognise as being separate. Linnaeus' system, based on sexual characteristics, Crocus was classified as Triandra Monogynia (Three , Single Gynoecium). Linnaeus's system was supplanted by the "natural" system which used a hierarchy of taxonomic ranks based on weighting of the importance of structural characteristics of the plant. Jussieu (1789) placed the genus Crocus in his Ordo (family) Irides or Les iris, as a member of the class Stamina epigyna (stamens inserted above the ovary) as part of the , the first level of the division of the . One of the first monographs of the genus appeared in 1809, by Haworth, followed in 1829 by that of Joseph Sabine, and Herbert in 1847. In 1853, John Lindley continued the placement of Crocus as one of 53 genera in Iridaceae, which he included in a higher order of monocotyledons, the Narcissales. Baker published a monograph on the genus in 1874, adopting a very different schema to that of Herbert. In 1883, Bentham and Hooker described the Irideae (Iridaceae) as having more than 700 species, and divided it into 3 tribes and further into subtribes. Tribe Sysyrinchieae as having 2 subtribes, including Ixieae. The latter was circumscribed with four genera, Crocus, Syringodea, Galaxia ( Moraea) and Romulea. This circumscription has remained stable since, with the exception of Moraea which properly belongs in a separate tribe. The most influential monograph of the nineteenth century was that of George Maw (1886), which forms the basis of modern understanding of the genus. Maw built on the work of Herbert, rejecting Baker's classification. The availability of molecular phylogenetic methods in the late twentieth century has shown that the Iridaceae properly belong within the order Asparagales.
Within the Romuleinae, Crocus is a sister group to Syringodea, the two genera forming a sister group to Romulea.
The most widely accepted system, that proposed by Brian Mathew in 1982 was based on Maw's system, but with less emphasis on flowering times. This mainly depended on three character states:
and included 81 species, however, one of these, Crocus medius was later recognized as a synonym of Crocus nudiflorus.The genus, as described by Mathew, consisted of two subgenera, Crocirus (monotypic for Crocus banaticus) and Crocus including the remainder of the species, based on whether the anthers were introrse or extrorse (dehiscence directed towards or away from centre of flower) respectively. Subgenus Crocus was then divided into two sections, Crocus and Nudiscapus, based on the presence or absence of the prophyll. Each section was then further divided into six series of Crocus and nine of Nudiscapus. These series were defined by the division of the style, the corm tunic, flowering time, leaf structure, presence of a bracteole and anther colour. Mathew also introduced the concept of subspecies, including 50 in all, by giving similar but different forms subspecies status if geographically separated, resulting in about 140 distinct taxa. The seven species and ten subspecies discovered since then have been integrated into revisions of this classification, though new species continue to be described, leading to estimates of at least 200 species.
Of the 15 series in the Mathew scheme, only seven were monophyletic, and in particular the largest series, Biflori and Reticulati, which include a third of all species, were non-monophyletic. Another anomalous species, C. baytopiorum, should now be placed in a series of its own, series Baytopi. C. gargaricus subsp. herbertii has been raised to species status, as C. herbertii. The autumn-flowering C. longiflorus, the type species of series Longiflori (long regarded by Mathew as "a disparate assemblage"), appeared to lie within series Verni. In addition, the position of C. malyi was currently unclear.
DNA analysis and morphological studies suggest further that series Reticulati, Biflori and Speciosi are "probably inseparable", C. adanensis and C. caspius should probably be removed from Biflori, C. adanensis falls in a clade with C. paschei as a sister group to the species of series Flavi and C. caspius appears to be sister to the species of series Orientales.
The study showed "no support for a system of sections as currently defined", although, despite the many inconsistencies between Mathew's 1982 classification and the current hypothesis, "the main assignment of species to the sections and series of that system is actually supported". The authors state, "further studies are required before any firm decisions about a hierarchical system of classification can be considered" and conclude "future re-classification is likely to involve all infrageneric levels, subgenera, sections and series". A further study, using the internal transcribed spacer region (ITS) of the nuclear ribosomal DNA (rDNA), together with a chloroplast marker, broadly confirmed these findings.
Crocus forms a monophyletic clade, with a basal polytomy of four subclades. The first clade (A) corresponding to section Crocus, but including C. sieberi and several closely related species (originally included in section Nudiscapus series Reticulati). The remaining three clades (B-D) include all the remaining species of section Nudiscapus. Of these, B and C are small, corresponding to series Orientales and Carpetani respectively, with all remaining series in the large D clade. The exception is C. caspius, originally in series Biflori, which segregates in clade B. Thus, although division of the genus into two sections is well supported, no single morphological character defines these two groups. The C. sieberi group are assumed to have lost their prophyll secondarily. Of the series, eight could be shown to be monophyletic; Crocus, Kotschyani and Scardici (section Crocus) and Aleppici, Carpetani, Laevigati, Orientalis and Speciosi (section Nudiscapus). Flowering season did not correspond to molecular groupings and nor did any of the previously used morphological characteristics, indicating a high degree of homoplasy, in which traits are gained or lost independently in different lineages. The remainder of the series could not be supported as natural groupings. Mathew's concept of subspecies status within C. biflorus could not be supported, each being considered a separate species, resulting in the genus having at least 150 species.
A more detailed molecular and morphological study of series Verni (section Crocus) allowed it to be better characterised and circumscribed, as well as the closely related series Longiflori. Series Verni sensu Mathew was found to consist of two groups, the first being C. vernus sensu Mathew and the other consisting of C. etruscus, ilvensis, kosaninii and longiflorus. The taxonomic status of C. vernus had been uncertain for some time, given the observation that the name was more properly applied to C. albiflorus, requiring a new designation of C. neapolitanus for those previously known as C. vernus. Subsequently C. vernus was split into 5 separate species. The incorporation of C. longiflorus into series Verni resulted in making series Longiflori no longer a legitimate taxonomic unit.
In section Nudiscapus, series Reticulati was polyphyletic with species intermingled with series Biflori and Speciosi, requiring a recircumscription, confining Reticulati to 8 species, to obtain monophyly. Among the thereby displaced species, are a number of very closely related taxa, referred to as the Crocus sieberi aggregate, which has been proposed as a new series Sieberi. Other new series, such as Isauri and Lyciotauri, continue to be created out of the Biflori series.
Mathew's circumscription of Crocus introduced the rank of subspecies, of which the largest number (14) were those of Crocus biflorus Philip Miller, the type species of series Biflori, a number which continued to grow. Molecular methods identified these as a polyphyletic assemblage rather than closely related subordinate infraspecific taxa. This necessitated a complete taxonomic revision of series Biflori, elevating each subspecies to species status. A similar issue occurs with C. reticulatus sensu Mathew, who created two subspecies, resulting in 9 newly defined species.
Some Pulsatilla species are also called "prairie crocus" (previously Anemone patens) or "wild crocus", but they belong to the buttercup family (Ranunculaceae). Pulsatilla species, which are commonly called pasqueflowers, unlike crocuses have , the foliage is covered with long soft hairs, and the flowers are produced on above-ground stems.
Habitats range from sea level to as high as subalpine altitudes, and in a wide range of habitats from woodlands to meadows and deserts, often on stony mountain slopes with good drainage. The majority of species are native to areas with cold winters and hot summers with little rain, and active growth is typically from fall to mid-spring. The natural habitats of crocus species are threatened by human activities, including urbanization, industrialization, and other land disturbances and recreational uses. They are negatively impacted by uncontrolled gathering and heavy grazing by livestock.
At night and in overcast weather, the perianth closes. The ovary produces nectar which attracts (particularly female ) and Lepidoptera.
Saffron is thought to have been used in embalming in Ancient Egypt. It is mentioned in the Old Testament, in the Song of Songs as a precious spice and has featured as a dye and fragrance throughout written history, with mention in the Iliad.
Cultivation and harvesting of C. sativus for saffron was first documented in the Mediterranean, notably on the island of Crete. showing them are found there at the Bronze Age Minoan site of Knossos, as well as from the comparably aged Akrotiri site on the Aegean Sea island of Santorini, and formed an important part of the Minoan economy and culture and had both a sacred role and use as a psychoactive drug and food additive. Women still gather crocuses in the Akrotiri region.
Crocuses are among the most important Ornamental plant geophytes in the global flower industry, ranking sixth in terms of Dutch bulb production (2003–2008) with 463–668 hectare under cultivation. The crocus is one of the most popular flowers found in the garden in the late winter and early spring. About 30 of the species are cultivated, among the most popular being C. chrysanthus, C. flavus, C. sieberi, C. tommasinianus and C. vernus, together with hundreds of cultivars derived from them. Both fall and spring blooming crocuses are cultivated for their flowers. Among the first flowers to bloom in spring, their flowering time can vary from fall to the late winter blooming C. tommasinianus; the earliest fall blooming species, C. scharojanii, may flower during the last weeks of July.
The varieties cultivated for decoration in gardens and pots mainly represent six species: C. vernus, C. chrysanthus, C. flavus, C. sieberi, C. speciosus and C. tommasinianus. During the horticulture production year 2009/2010, more than 70 cultivars were grown in Holland, covering an area of 366 ; the most common ones were 'Flower Record' and 'King of the Stripes' which accounted for 42 hectares, other species grown included C. chrysanthus, C. tommasinianus, and C. flavus - all are spring blooming plants. But the most commonly grown plants are the Dutch hybrids with large flowers in a rich palette of colors.
Both sexual and asexual means are used to increase the number of plants; seeds and multiplication of corms are the most common means of production, but tissue culture can be used, most commonly for saffron crocus. New corms are formed on top of the older corm which withers away, and cormels are produced from axillary buds. The production of new plants begins with harvested corms in late June to early July, after being graded by corm size the corms are stored around 22 Celsius until early October when they are moved to 17 Celsius until planted later in October and November; flowering occurs in March and the flowers are not removed. Crocuses are also forced to produce flowering plants out of season and the most common species used are C. vernus and C. flavus, and most of the corms used for forcing come from the Netherlands.
Spring flowering types are planted in fall, while fall-blooming types in late summer; typically, the corms are placed 3 to 4 inches deep in well-draining soil in areas with full sun exposure. They do not thrive in heavy clay soils or those that are damp, especially during their summer dormancy period. Commercial crops are produced on raised beds and slopes, to ensure adequate drainage, while horticulturalists often plant on sand beds for the same purpose. Spring flowering types also do well in areas with deciduous trees, where they flower and produce leaves before the trees completely leaf-out. Crocuses are grown in USDA winter zones 3–8. Not all species are hardy in the upper zones; C. sativus is winter hardy in USDA zones 6 through 8, and C. pulchellus is hardy in zones 5 through 8.
Some are suitable for naturalizing in grass, but mowing off the foliage before it turns yellow produces short lived plants. Some crocuses, especially C. tommasinianus and its selected forms and hybrids (such as 'Whitewell Purple' and 'Ruby Giant'), seed prolifically and are ideal for naturalizing. They can, however, become weeds in , where they will often appear in the middle of choice, mat-forming alpine plants, and can be difficult to remove. Crocus flowers and leaves are protected from frost by a waxy cuticle; in areas where snow and frost occasionally occur in the early spring, it is not uncommon to see early flowering crocuses blooming through a light late snowfall.
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C. laevigatus has a long flowering period which starts in late autumn or early winter and may continue into February.
Colchicum autumnale is commonly known as "autumn crocus", but is a member of the plant family Colchicaceae, and not a true crocus (of the family Iridaceae).
Crocuses occur in many flower paintings, one of the earliest being that of Ambrosius Bosschaert's Composed Bouquet of Spring Flowers (1620). In this painting the cream-colored crocus feathered with bronze at the base of the bouquet reflected varieties on the market at that time. Bosschaert, working from a preparatory drawing to paint his composed piece spanning the whole of spring, exaggerated the crocus so that it passes for a tulip, but its narrow, grass-like leaves give it away.
The crocus is used in many contexts to symbolically denote spring and new beginnings. For instance, it was used as the emblem of the 2019 FIFA U-20 World Cup in Poland to symbolise the emergence of new talent.
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