1 Evolution, Domestication and Taxonomy

1 Evolution, Domestication and Taxonomy R.M. Fritsch1 and N. Friesen2 1Institut für Pflanzengenetik und Kulturpflanzenforschung, D-06466 Gatersleben, Germany; 2Botanischer Garten der Universität, D-49076 Osnabrück, Germany 1. The Genus Allium L. 5 1.1 General characteristics 5 1.2 Distribution, ecology and domestication 6 1.3 Phylogeny and classification 10 2. The Section Cepa (Mill.) Prokh. 14 2.1 Morphology, distribution and ecology 14 2.2 Cytological limitations 15 2.3 Grouping of the species 15 2.4 Enumeration of the species 16 3. Allium cepa L. 19 3.1 Description and variability 19 3.2 Infraspecific classification 20 3.3 Evolutionary lineages 21 3.4 History of domestication and cultivation 22 4. Other Economic Species 23 4.1 Garlic and garlic-like forms 23 4.2 Taxa of Asiatic origin 24 4.3 Chives and locally important onions from other areas 25 5. Conclusions 26 Acknowledgements 27 References 27 1. The Genus Allium L. controversy. In early classifications of the angiosperms (Melchior, 1964), they were 1.1 General characteristics placed in the Liliaceae. Later, they were more often included in the Amaryllidaceae, The taxonomic position of Allium and on the basis of inflorescence structure. related genera has long been a matter of Recently, molecular data have favoured a © CAB International 2002. Allium Crop Science: Recent Advances (eds H.D. Rabinowitch and L. Currah) 5 6 R.M. Fritsch and N. Friesen division into a larger number of small mono- • Ovary: trilocular, three septal nectaries of phyletic families. In the most recent and various shape, two or more curved competent taxonomic treatment of the (campylotropous) ovules per locule, monocotyledons, Allium and its close rela- sometimes diverse apical appendages tives were recognized as a distinct family, the (crests and horns); developing into a Alliaceae, close to the Amaryllidaceae. The fol- loculicidal capsule dehiscing along the lowing hierarchy has been adopted midrib of the carpels. (Takhtajan, 1997): • Style: single, with slender, capitate or, more rarely, trilobate stigma. 1. Class Liliopsida. • Seeds: angular to globular, black (epider- 2. Subclass Liliidae. mal layer contains phytomelan), orna- 3. Superorder Liliianae. mentation of the cells extremely variable. 4. Order Amaryllidales. • Chemical characters: reserve compounds 5. Family Alliaceae. consist of sugars, mainly fructans, and no 6. Subfamily Allioideae. starch; enzymatic decomposition prod- 7. Tribe Allieae. ucts of several cysteine sulphoxides (see 8. Genus Allium. Randle and Lancaster, Chapter 14, and However, other classifications still have their Keusgen, Chapter 15, this volume) cause proponents and are still used in some litera- the species- and group-specific (though ture. sometimes missing) characteristic odour. There is more agreement about the • Karyology: predominant basic chromo- delimitation of the genus Allium itself. It is a some numbers x = 8 and x = 7 with large genus of perennial, mostly bulbous polyploids in both series; chromosome plants sharing as characteristics: morphology and banding pattern different between taxonomic groups. • Underground storage organs: bulbs, rhizomes or swollen roots. Shape, size, colour and texture of rhi- • Bulbs: often on rhizomes; true bulbs (one zomes, bulbs, roots, leaves (e.g. flat, chan- or two extremely thickened prophylls) or nelled, terete or fistulose, sheath/lamina false bulbs (thickened basal sheaths plus ratio), scapes, spathes, inflorescences, tepals thickened prophylls (bladeless ‘true (mostly white or rose to violet, rarely blue or scales’)); several tunics, membranous, yellow), stamens, ovaries and seeds may vary fibrous or coriaceous; annual or peren- considerably and in very different manners. nial roots. The same is true for the anatomy, cross- • Rhizomes: condensed or elongated; sections and internal structure of all the rarely runner-like; with very diverse listed plant parts. branching patterns. Basal bulblets and bulbils (topsets) are • Leaves: basally arranged, frequently cov- important in vegetative propagation. As far ering the flower scape and thus appear- as known, most Allium species are alloga- ing cauline. mous. Spontaneous interspecific hybridiza- • Bracts: two to several, often fused into an tion is not as rare as formerly believed, but involucre (‘spathe’). strong crossing barriers exist in some • Inflorescence: fasciculate to often umbel- groups, even between morphologically simi- or head-like, (one-) few- to many-flowered, lar species. loose to dense. • Flowers: pedicelled, actinomorphic, hypogynous, trimerous. 1.2 Distribution, ecology and • Tepals: in two slightly differentiated domestication whorls, free. • Stamens: in two whorls, sometimes The genus Allium is widely distributed over basally connected, the inner ones often the holarctic region from the dry subtropics widened and/or toothed. to the boreal zone (Fig. 1.1). One or two Evolution, Domestication and TaxonomyEvolution, Domesticationand 7 Fig. 1.1. World distribution of wild species of the genus Allium. The numbers on the map indicate the number of species found in each region. 8 R.M. Fritsch and N. Friesen species even occur in the subarctic belt, e.g. However, in contrast, some Allium species A. schoenoprasum L., and a few alliums are are noxious weeds of cultivated ground. The scattered in mountains or highlands within cultivated Allium crop species are listed in the subtropics and tropics. Only A. Table 1.1. dregeanum Kth. has been described from the Generally, all plant parts of alliums may southern hemisphere (South Africa) (de be consumed by humans (except perhaps Sarker et al., 1997). the seeds), and many wild species are A region of especially high species diver- exploited by the local inhabitants. These sity stretches from the Mediterranean basin natural resources are often improperly man- to Central Asia and Pakistan (Fig. 1.1). A sec- aged at the present time (see Section 2.3.4), ond, less pronounced centre of species and overcollecting caused severe decline of diversity occurs in western North America. wild sources in the past. Very probably, both These centres of diversity possess differing protection and the rational use of wild percentages of the several subgroups of the plants growing close to settlements, as well genus and are thus clearly distinguishable in as the transfer of plants into existing garden taxonomic terms. plots (as explained below under A. cepa) Evolution of the genus has been accompa- (Hanelt, 1990), may all have been important nied by ecological diversification. The major- at the initial stages of domestication. Further ity of species grow in open, sunny, rather dry human and natural selection then led to the sites in arid and moderately humid climates. development of the different plant types However, Allium species have adapted to present in several cultivated species. many other ecological niches. Different types Domestication did not change the ploidy of forests, European subalpine pastures and status of onion, shallot, garlic and many other moist subalpine and alpine grasslands of the diploid species, and introgression of other Himalayan and Central Asian high moun- species only rarely played a role during the tains all contain some Allium species, and selection processes. The same seems to be gravelly places along river-banks do as well. true for the cultivated taxa of A. ampeloprasum, Even saline and alkaline environments are which apparently arose from ancestors of dif- tolerated by some taxa. ferent ploidy levels (see Section 4.2). Allium species from these diverse habitats However, cultivated strains of A. ramosum exhibit a parallel diversity in their rhythms of and A. chinense include diploids, triploids growth (phenology). Spring-, summer- and and tetraploids. Because diploid and autumn-flowering taxa exist. There are tetraploid wild strains exist, polytopic, i.e. at short- and long-living perennials, species with different places (and at several times), one or several annual cycles of leaf formation, domestication of A. ramosum seems probable. and even continuously leafing ones. Species The history of domestication of A. chinense is may show summer or winter dormancy. For still being disputed. Either the existence of many species (named ‘ephemeroids’), annual wild strains in Central and East China is growth is limited to a very short period in accepted, or cultivars are traced back to the spring and early summer when the cycle closely related wild species A. komarovianum from leaf sprouting to seed maturation is Vved. Participation of other wild species, completed in 2 or 3 months. such as A. thunbergii G. Don, seems possible Conditions suitable for seed germination (Hanelt, 2001). vary between species. Seed dormancy is vari- Domestication of wild plants is still con- able between wild species. For most species tinuing. A. komarovianum was reportedly the germinability of the seeds seems to be taken again into cultivation as a vegetable in limited to a few years, unless the seed is North Korea quite recently (Hanelt, 2001), stored under cold and very dry conditions, and the case of A. pskemense is described when its life can be greatly extended. below (Section 3.4). Some species listed The genus is of great economic signifi- below (Section 4) have also been recently cance because it includes several important taken into cultivation, but usually exact data vegetable crops and ornamental species. are lacking. Evolution, Domestication and Taxonomy 9 Table 1.1. Cultivated Allium species and their areas of cultivation. Botanical

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