A numerical taxonomic analysis of the Daucus carota complex

Abstract

A variety of numerical taxonomic procedures was employed to assess variation of 437 diverse populations of Daucus carota sensu lato, grown under controlled conditions, and of 100 herbarium sheets. The domesticated plants proved to be sharply discontinuous from the wild plants. In contrast with wild plants, domesticated plants possess relatively brittle, palatable, pigmented, larger, unbranched storage organs, fewer but larger relatively erect leaves, strict biennialness, larger fruits, comparatively rapid growth, relatively foliose involucral bracts, fewer central purple flowers in the umbels, smaller petals, fewer fruit spines, brittle mericarp spine hooks, and basally branched primary mericarp bristles. The first 11 differences are interpreted as the direct or indirect results of directional selection by man. The last six differences are hypothesized to be changes resulting from lack of stabilizing selection for characters of value in the wild. Domesticated carrots range from primitive Asian ('eastern') variants with yellow and purple storage organs and poorly dissected gray–green pubescent foliage to the familiar advanced type of ('western') cultivar with orange roots and highly dissected, relatively unpubescent yellow–green foliage. Numerical analysis indicated that an uninterrupted spectrum of variants connect these two kinds, and whereas two comprehensive groups of cultigens are distinguishable, any line of demarcation is arbitrary. The two kinds of cultigens are recognized as D. carota subsp. sativus var. sativus ('western carrot') and D. carota subsp. sativus var. atrorubens ('eastern carrot'). Wild carrots proved to be separable into two overlapping comprehensive groups, which were informally labelled subspecies aggregate gingidium and subspecies aggregate carota (the latter assemblage also encompassing the cultigens). Subsp. agg. carota primarily includes cosmopolitan weedy variants, some of which may have contributed germplasm to the cultivars. More importantly, this group contains an inconspicuously differentiated Asian subgroup which was found likely to represent the primary ancestor of the domesticated carrot, as evidenced by similarity with the primitive cultigens studied.