88 – II.2. SQUASHES, PUMPKINS, ZUCCHINIS, GOURDS (CURCURBITA SPECIES)
two subspecies: 1) ssp. pepo, composed of two varieties: var. pepo, in which all edible
cultivars are included, and var. fraterna, corresponding to the wild ancestor of this part of
the group; and 2) ssp. ovifera, also with two varieties: var. ovifera, which includes
cultivars used as decoration, and var. texana. The second classification (Andres, 1987a)
is simpler and proposes that C. pepo is only constituted by three subspecies: ssp. pepo,
which includes all edible and ornamental cultivated types, and the subspecies texana and
fraterna, in which the wild ancestors of the group are located. The third proposal
(Decker-Walters et al., 1993) is a modification of the first, as it has three subspecies: ssp.
pepo, which includes local races and commercial cultivars, ssp. fraterna and ssp. ovifera.
Under this proposal, subspecies ovifera is composed of three varieties: 1) var. ozarkana
(wild plants in the states of Arkansas, Illinois, Louisiana, Missouri and Oklahoma in the
United States), 2) var. texana (wild plants in the states of Louisiana, Mississippi,
New Mexico and Texas in the United States), and 3) var. ovifera (mainly ornamental
cultivars). For simplicity, this chapter, in developing the C. pepo grouping in Table 2.1,
follows the classification proposed by Andres (1987a), but recognises that the
classification is still in flux as new molecular information is developed, as discussed
below.
Work by Wilson, Doebley and Duvall in 1992 using restriction fragment length
polymorphism analysis on 15 species in the genus supports the separation of cultivars of
C. pepo into two distinct lineages, C. pepo ssp. pepo and C. pepo ssp. ovifera, as do
isozyme studies of these taxa (Decker-Walters et al., 1993; Jobst, King and Hemleben,
1998). Analysis of the sequence of an intron of the mitochondrial nad1 gene has also
been used to elucidate the relationship between the various members of the Pepo group
(Sanjur et al., 2002), and this analysis also suggests that C. pepo can be subdivided into
two subspecies: C. pepo ssp. pepo and C. pepo ssp. ovifera.
Smith (2006) agrees that C. pepo is comprised of two subspecies: C. pepo ssp. pepo
and C. pepo ssp. ovifera. C. pepo ssp. pepo includes pumpkin, zucchini and other marrow
squashes, Mexican landraces and a few ornamental gourds. C. pepo ssp. ovifera
comprises both domesticated and free-living populations, and is further divided into
three taxa: C. pepo ssp. ovifera var. ovifera, which includes some cultivars (e.g. acorn,
crookneck and scallop squash and some pumpkin) and most ornamental gourds; and the
free-living populations in the United States, which represent two molecularly distinct
populations; C. pepo ssp. ovifera var. texana and C. pepo ssp. ovifera var. ozarkana
(Decker-Walters et al., 1993, 2002).
The analysis by Sanjur et al. (2002) of an intron of the mitochondrial nad1 gene
shows that C. fraterna, C. pepo var. texana, C. pepo var. ozarkana and cultivated C. pepo
ssp. ovifera form a closely related clade, with any of the three wild species a potential
progenitor of the domesticated species. The C. pepo ssp. pepo lineage is separated from
the ovifera clade on the basis of a three base pair difference in an intron of the gene nad1
of the mitochondrial DNA, a finding which supports the hypothesis that C. pepo ssp. pepo
and C. pepo ssp. ovifera arose from two separate domestication events.
All of the C. pepo subspecies and variants can successfully hybridise with each other,
suggesting that the C. pepo progenitors for both subspecies pepo and ovifera were once
part of an extended contiguous population reaching from Mexico through the eastern
United States. Whether this extended range occurred naturally or was influenced by
humans is still uncertain (Newsom, Webb and Dunbar, 1993; Smith, 2006).
Upon reviewing archaeological evidence found in the state of Florida (United States),
Hart, Daniels and Sheviak (2004) suggest that the pepo gourd may have first been
