Cucurbita
is a genus of herbaceous fruits in the gourd family, Cucurbitaceae, native to the Andes and Mesoamerica. Five edible species are grown and consumed for their flesh and seeds. They are variously known as squash, pumpkin, or gourd, depending on species, variety, and local parlance. Other kinds of gourd, also called bottle-gourds, are native to Africa and belong to the genus Lagenaria, which is in the same family and subfamily as Cucurbita, but in a different tribe; their young fruits are eaten much like those of the Cucurbita species.
There is debate about the taxonomy of the genus and the number of accepted species varies from 13 to 30. The five domesticated species are Cucurbita argyrosperma, C. ficifolia, C. maxima, C. moschata, and C. pepo, all of which can be treated as winter squash because the full-grown fruits can be stored for months. However, C. pepo includes some cultivars that are better used only as summer squash.
Most Cucurbita species are herbaceous vines that grow several meters in length and have tendrils, but non-vining "bush" cultivars of C. pepo and C. maxima have also been developed. The yellow or orange flowers on a Cucurbita plant are of two types: female and male. The female flowers produce the fruit and the male flowers produce pollen. Many North and Central American species are visited by specialist bee pollinators, but other insects with more general feeding habits, such as honey bees, also visit.
The fruits of the genus Cucurbita are good sources of nutrients, such as vitamin A and vitamin C, among other nutrients according to species. The fruits have many culinary uses including pumpkin pie, biscuits, bread, desserts, puddings, beverages, and soups; they are now cultivated worldwide. Although botanical fruits, Cucurbita gourds such as squash are typically cooked and eaten as vegetables. Pumpkins see more varied use, and are eaten both as vegetables and as desserts such as pumpkin pie.
Description
Cucurbita species fall into two main groups. The first group consists of annual or short-lived perennial vines which are mesophytic, meaning they require a more or less continuous water supply. The second group are perennials growing in arid zones which are xerophytic, meaning they tolerate dry conditions. Cultivated Cucurbita species were derived from the first group. Growing in height or length, the plant stem produces tendrils to help it climb adjacent plants and structures or extend along the ground. Most species do not readily root from the nodes; a notable exception is C. ficifolia, and the four other cultivated mesophytes do this to a lesser extent. The vine of the perennial Cucurbita can become semiwoody if left to grow. There is wide variation in size, shape, and color among Cucurbita fruits, and even within a single species. C. ficifolia is an exception, being highly uniform in appearance. The morphological variation in the species C. pepo and C. maxima is so vast that its various subspecies and cultivars have been misidentified as totally separate species.The typical cultivated Cucurbita species has five-lobed or palmately divided leaves with long petioles, with the leaves alternately arranged on the stem. The stems in some species are angular. All of the above-ground parts may be hairy with various types of trichomes, which are often hardened and sharp. Spring-like tendrils grow from each node and are branching in some species. C. argyrosperma has ovate-cordate leaves. The shape of C. pepo leaves varies widely. C. moschata plants can have light or dense pubescence. C. ficifolia leaves are slightly angular and have light pubescence. The leaves of all four of these species may or may not have white spots.
The species are monoecious, with unisexual male and female flowers on a single plant and these grow singly, appearing from the leaf axils. Flowers have five fused yellow to orange petals and a green bell-shaped calyx. Male flowers in Cucurbitaceae generally have five stamens, but in Cucurbita there are only three, and their anthers are joined so that there appears to be one. Female flowers have thick pedicels, and an inferior ovary with 3–5 stigmas that each have two lobes. The female flowers of C. argyrosperma and C. ficifolia have larger corollas than the male flowers. Female flowers of C. pepo have a small calyx, but the calyx of C. moschata male flowers is comparatively short.
Cucurbita fruits are large and fleshy. Botanists classify the Cucurbita fruit as a pepo, which is a special type of berry derived from an inferior ovary, with a thick outer wall or rind with hypanthium tissue forming an exocarp around the ovary, and a fleshy interior composed of mesocarp and endocarp. The term "pepo" is used primarily for Cucurbitaceae fruits, where this fruit type is common, but the fruits of Passiflora and Carica are sometimes also pepos. The seeds, which are attached to the ovary wall and not to the center, are large and fairly flat with a large embryo that consists almost entirely of two cotyledons. Fruit size varies considerably: wild fruit specimens can be as small as and some domesticated specimens can weigh well over. The current world record was set in 2014 by Beni Meier of Switzerland with a pumpkin.
Reproductive biology
All species of Cucurbita have 20 pairs of chromosomes.Many North and Central American species are visited by specialist pollinators in the apid tribe Eucerini, especially the genera Peponapis and Xenoglossa, and these squash bees can be crucial to the flowers producing fruit after pollination.
When there is more pollen applied to the stigma, more seeds are produced in the fruits and the fruits are larger with greater likelihood of maturation, an effect called xenia. Competitively grown specimens are therefore often hand-pollinated to maximize the number of seeds in the fruit. Seedlessness is known to occur in certain cultivars of C. pepo.
Critical factors in flowering and fruit set are physiological, having to do with the age of the plant and whether it already has developing fruit. The plant hormones ethylene and auxin are key in fruit set and development. Ethylene promotes the production of female flowers. When a plant already has a fruit developing, subsequent female flowers on the plant are less likely to mature, a phenomenon called "first-fruit dominance", and male flowers are more frequent, an effect that appears due to reduced natural ethylene production within the plant stem. Ethephon, a plant growth regulator product that is converted to ethylene after metabolism by the plant, can be used to increase fruit and seed production. Although Cucurbita species can generally produce healthy fruit after pollination from the same plant, inbreeding depression can significantly reduce seed number and fruit size.
The plant hormone gibberellin, produced in the stamens, is essential for the development of all parts of the male flowers. The development of female flowers is not yet understood. Gibberellin is also involved in other developmental processes of plants, such as seed and stem growth.
Germination and seedling growth
Seeds with maximum germination potential develop by 45 days after anthesis, and seed weight reaches its maximum 70 days after anthesis. Some varieties of C. pepo germinate best with eight hours of sunlight daily and a planting depth of. Seeds planted deeper than are not likely to germinate. In C. foetidissima, a weedy species, plants younger than 19 days old are not able to sprout from the roots after removing the shoots. In a seed batch with 90 percent germination rate, over 90 percent of the plants had sprouted after 29 days from planting.Experiments have shown that when more pollen is applied to the stigma, as well as the fruit containing more seeds and being larger, the germination of the seeds is also faster and more likely, and the seedlings are larger. Various combinations of mineral nutrients and light have a significant effect during the various stages of plant growth. These effects vary significantly between the different species of Cucurbita. A type of stored phosphorus called phytate forms in seed tissues as spherical crystalline intrusions in protein bodies called globoids. Along with other nutrients, phytate is used completely during seedling growth. Heavy metal contamination, including cadmium, has a significant negative impact on plant growth. Cucurbita plants grown in the spring tend to grow larger than those grown in the autumn.
Taxonomy
Cucurbita was formally described in a way that meets the requirements of modern botanical nomenclature by Linnaeus in his Genera Plantarum, the fifth edition of 1754 in conjunction with the 1753 first edition of Species Plantarum. Cucurbita pepo is the type species of the genus. Linnaeus initially included the species C. pepo, C. verrucosa and C. melopepo, as well as C. citrullus and C. lagenaria has been used as an intermediary, as it can be crossed with all the common Cucurbita.Various taxonomic treatments have been proposed for Cucurbita, ranging from 13 to 30 species. In 1990, Cucurbita expert Michael Nee classified them into the following oft-cited 13 species groups, listed by group and alphabetically, with geographic origin:
- C. argyrosperma – cushaw pumpkin; origin: Mexico
- * C. kellyana, origin: Pacific coast of western Mexico
- * C. palmeri, origin: Pacific coast of northwestern Mexico
- * C. sororia, origin: Pacific coast Mexico to Nicaragua, northeastern Mexico
- C. digitata – fingerleaf gourd; origin: southwestern United States, northwestern Mexico
- * C. californica
- * C. cordata
- * C. cylindrata
- * C. palmata
- C. ecuadorensis, origin: Ecuador's Pacific coast
- C. ficifolia – figleaf gourd, chilacayote, alcayota; origin: Mexico, Panama, northern Chile and Argentina
- C. foetidissima – stinking gourd, buffalo gourd; origin: Mexico
- * C. scabridifolia, likely a natural hybrid of C. foetidissima and C. pedatifolia
- C. galeottii, little known; origin: Oaxaca, Mexico
- C. lundelliana, origin: Mexico, Guatemala, Belize
- C. maxima – winter squash, pumpkin; origin: Argentina, Bolivia, Ecuador
- * C. andreana, origin – Argentina
- C. moschata – butternut squash, 'Dickinson' pumpkin, golden cushaw; origin: Bolivia, Colombia, Ecuador, Mexico, Panama, Puerto Rico, Venezuela
- C. okeechobeensis, origin: Florida
- * C. martinezii, origin: Mexican Gulf Coast and foothills
- C. pedatifolia, origin: Querétaro, Mexico
- * C. moorei
- C. pepo – field pumpkin, summer squash, zucchini, vegetable marrow, courgette, acorn squash; origin: Mexico, US
- * C. fraterna, origin: Tamaulipas and Nuevo León, Mexico
- * C. texana, origin: Texas, US
- C. radicans – calabacilla, calabaza de coyote; origin: Central Mexico
- * C. gracilior
- C. digitata, C. palmata, C. californica, C. cylindrata, C. cordata
- C. martinezii, C. okeechobeensis, C. lundelliana
- C. sororia, C. gracilior, C. palmeri; C. argyrosperma was considered close to the three previous species
- C. maxima, C. andreana
- C. pepo, C. texana
- C. moschata, C. ficifolia, C. pedatifolia, C. foetidissima, and C. ecuadorensis were placed in their own separate species groups as they were not considered significantly close to any of the other species studied.