As Gossypium diversified, so did seed and
Extant species exhibit extraordinary variation in seed size
and in the length, color, and density of the layer of single-celled trichomes
on the seed surface. Seed coverings range from nearly glabrous (e.g., G. klotzschianum
and G. davidsonii), to short (several mm) stiff, brown hairs that aid in wind-dispersal (G. australe,
G. nelsonii), to the long, fine white fibers that characterize improved forms of the four cultivated species.
In all but the modern forms of the domesticated species, seed fibers are adherent to the seed coat. As noted above,
a parallel domestication involved two species from the Americas, G. hirsutum and G. barbadense, and
two from Africa-Asia, G. arboreum and G. herbaceum. In each case, aboriginal peoples discovered
thousands of years ago that the unique properties of cotton fibers made them useful for ropes, textiles and other
applications. A notable aspect of this history is that similar domestication processes resulted in apparently
similar morphological transformations, including decreased plant stature,
loss of photoperiod sensitivity, loss of seed dormancy, and most notably, a
dramatic increase in the abundance, length, and quality of seed epidermal fiber.
Gossypium hirsutum presently accounts for >90% of
the global cotton crop, having spread from its ancestral home in Mesoamerica to over 50 countries in both hemispheres.
The following image, provided by Cotton Incorporated, summarizes
the range of morphological diversity exhibited by members of the
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