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Squash
Various sizes, shapes, and colors of Cucurbita
Cucurbita fruits come in an assortment of colors and sizes.
Scientific classification
Synonyms
  • Mellonia Gasp.
  • Melopepo Mill.
  • Ozodycus Raf.
  • Pepo Mill.
  • Pileocalyx Gasp.
  • Sphenantha Schrad.
  • Tristemon Scheele 1848, illegitimate homonym, not Raf. 1819 (Juncaginaceae) nor Raf. 1838 (Juncaceae) nor Klotzsch 1838 (Ericaceae)

Cucurbita (Latin for gourd) is a genus of herbaceous vines in the gourd family, Cucurbitaceae (also known as cucurbits or cucurbi) native to the Andes and Mesoamerica. Five species are grown worldwide for their edible fruit, variously known as squash, pumpkin, or gourd, depending on species, variety, and local parlance, and for their seeds. 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. These other gourds are used as utensils or vessels, and their young fruits are eaten much like those of Cucurbita species.

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.

There is debate about the taxonomy of the genus, as 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 these 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.

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.

Description

Cucurbita 2011 G1
C. pepo pumpkins – the two bright orange ones in center right, and squashes C. maxima, all others

Cucurbita species fall into two main groups. The first group are annual or short-lived perennial vines and are mesophytic, i.e. they require a more or less continuous water supply. The second group are perennials growing in arid zones and so are xerophytic, tolerating dry conditions. Cultivated Cucurbita species were derived from the first group. Growing 5 to 15 meters (16 to 49 ft) 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.

Cucurbita moschata leaves
The leaves of Cucurbita moschata often have white spots near the veins.

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 (egg-shaped to heart-shaped) 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.

There are male (staminate) and female (pistillate) flowers (unisexual flowers) on a single plant (monoecious), and these grow singly, appearing from the leaf axils. Flowers have five fused yellow to orange petals (the corolla) 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 together 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.

2016-11-10 Cucurbits (Cucurbitaceae) Madrid Botanico
A variety of fruits displayed at the Real Jardín Botánico de Madrid in 2016

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 (parietal placentation) 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 4 centimeters (1.6 in) and some domesticated specimens can weigh well over 300 kilograms (660 lb). The current world record was set in 2014 by Beni Meier of Switzerland with a 2,323.7-pound (1,054.0 kg) pumpkin.

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 (both now included in C. pepo), as well as C. citrullus (watermelon, now Citrullus lanatus) and C. lagenaria (now Lagenaria siceraria) (both are not Cucurbita but are in the family Cucurbitaceae.

The Cucurbita digitata, C. foetidissima, C. galeotti, and C. pedatifolia species groups are xerophytes, arid zone perennials with storage roots; the remainder, including the five domesticated species, are all mesophytic annuals or short-life perennials with no storage roots. The five domesticated species are mostly isolated from each other by sterility barriers and have different physiological characteristics. Some cross pollinations can occur: C. pepo with C. argyrosperma and C. moschata; and C. maxima with C. moschata. Cross pollination does occur readily within the family Cucurbitaceae. The buffalo gourd (C. foetidissima), which; according to some, does not taste good, has been used as an intermediary as it can be crossed with all the common Cucurbita.

2006-10-18Cucurbita pepo06
An assortment of fruits of C. maxima and C. pepo

Various taxonomic treatments have been proposed for Cucurbita, ranging from 13–30 species. In 1990, Cucurbita expert Michael Nee classified them into the following oft-cited 13 species groups (27 species total), listed by group and alphabetically, with geographic origin:

  • C. argyrosperma (synonym C. mixta) – cushaw pumpkin; origin: Panama, 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 (USA), northwestern Mexico
    • C. californica
    • C. cordata
    • C. cylindrata
    • C. palmata
  • C. ecuadorensis, origin: Ecuador's Pacific coast
  • C. ficifolia – figleaf gourd, chilacayote; 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 is 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, USA
  • C. radicans – calabacilla, calabaza de coyote; origin: Central Mexico
    • C. gracilior

The taxonomy by Nee closely matches the species groupings reported in a pair of studies by a botanical team led by Rhodes and Bemis in 1968 and 1970 based on statistical groupings of several phenotypic traits of 21 species. Seeds for studying additional species members were not available. Sixteen of the 21 species were grouped into five clusters with the remaining five being classified separately:

  • C. digitata, C. palmata, C. californica, C. cylindrata, C. cordata
  • C. martinezii, C. okeechobeensis, C. lundelliana
  • C. sororia, C. gracilior, C. palmeri; C. argyrosperma (reported as C. mixta) 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.

Phylogeny

The full phylogeny of this genus is unknown, and research was ongoing in 2014. The following cladogram of Cucurbita phylogeny is based upon a 2002 study of mitochondrial DNA by Sanjur and colleagues.



Sechium edule




C. ficifolia




C. foetidissima





C. maxima and C. andreana



C. ecuadorensis





C. martinezii




C. pepo subspp. fraterna and ovifera




C. pepo subsp. pepo




C. sororia, in part




C. moschata



C. sororia, in part and C. argyrosperma












Reproductive biology

Peponapis pruinosaCane-12
Cucurbita female flower with pollinating squash bees

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.

Cucurbita maxima Zapallo Plomo semillería Costanzi - flowers detail (masculine) - male flower, some petals and 1 filament removed
Male flower, part of the perianth and one filament removed

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, which increases the fruit size; this pollination requires skilled technique. Seedlessness is known to occur in certain cultivars of C. pepo.

The most 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.

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

Kabocha (GH) 21June2005 sown 14June
Kabocha seedling seven days after being sown

Seeds with maximum germination potential develop (in C. moschata) 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 1.2 centimeters (0.47 in). Seeds planted deeper than 12.5 centimeters (4.9 in) 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 xenia effect mentioned above), 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.

Distribution and habitat

2009 Circleville Pumpkin Show champions
A festival-winning pumpkin in 2009 weighing 742 kilograms (1,636 lb)

Archaeological investigations have found evidence of domestication of Cucurbita going back over 8,000 years from the very southern parts of Canada down to Argentina and Chile. Centers of domestication stretch from the Mississippi River watershed and Texas down through Mexico and Central America to northern and western South America. Of the 27 species that Nee delineates, five are domesticated. Four of them, C. argyrosperma, C. ficifolia, C. moschata, and C. pepo, originated and were domesticated in Mesoamerica; for the fifth, C. maxima, these events occurred in South America.

Within C. pepo, the pumpkins, the scallops, and possibly the crooknecks are ancient and were domesticated at different times and places. The domesticated forms of C. pepo have larger fruits than non-domesticated forms and seeds that are bigger but fewer in number. In a 1989 study on the origins and development of C. pepo, botanist Harry Paris suggested that the original wild specimen had a small round fruit and that the modern pumpkin is its direct descendant. He suggested that the crookneck, ornamental gourd, and scallop are early variants and that the acorn is a cross between the scallop and the pumpkin.

Cucurbita moschata Butternut 2012 G2
C. moschata 'Butternut'

C. argyrosperma is not as widespread as the other species. The wild form C. a. subsp. sororia is found from Mexico to Nicaragua, and cultivated forms are used in a somewhat wider area stretching from Panama to the southeastern United States. It was probably bred for its seeds, which are large and high in oil and protein, but its flesh is of poorer quality than that of C. moschata and C. pepo. It is grown in a wide altitudinal range: from sea level to as high as 1,800 meters (5,900 ft) in dry areas, usually with the use of irrigation, or in areas with a defined rainy season, where seeds are sown in May and June.

C. ficifolia and C. moschata were originally thought to be Asiatic in origin, but this has been disproven. The origin of C. ficifolia is Latin America, most likely southern Mexico, Central America, or the Andes. It grows at altitudes ranging from 1,000 meters (3,300 ft) to 3,000 meters (9,800 ft) in areas with heavy rainfall. It does not hybridize well with the other cultivated species as it has significantly different enzymes and chromosomes.

C. maxima originated in South America over 4,000 years ago, probably in Argentina and Uruguay. The plants are sensitive to frost, and they prefer both bright sunlight and soil with a pH of 6.0 to 7.0. C. maxima did not start to spread into North America until after the arrival of Columbus. Varieties were in use by native peoples of the United States by the 16th century. Types of C. maxima include triloba, zapallito, zipinka, Banana, Delicious, Hubbard, Marrow (C. maxima Marrow), Show, and Turban.

Cucurbita moschata 'Tromboncino'
Fruit of the 'Tromboncino' cultivar of the Crookneck (C. moschata) Group are eaten either when very young, or as mature winter squash.

C. moschata is native to Latin America, but the precise location of origin is uncertain. It has been present in Mexico, Belize, Guatemala, and Peru for 4,000–6,000 years and has spread to Bolivia, Ecuador, Panama, Puerto Rico, and Venezuela. This species is closely related to C. argyrosperma. A variety known as the Seminole Pumpkin has been cultivated in Florida since before the arrival of Columbus. Its leaves are 20 to 30 centimeters (8 to 12 in) wide. It generally grows at low altitudes in hot climates with heavy rainfall, but some varieties have been found above 2,200 meters (7,200 ft). Groups of C. moschata include Cheese, Crookneck (C. moschata), and Bell.

C. pepo is one of the oldest, if not the oldest, domesticated species with the oldest known locations being Oaxaca, Mexico, 8,000–10,000 years ago, and Ocampo, Tamaulipas, Mexico, about 7,000 years ago. It is known to have appeared in Missouri, United States, at least 4,000 years ago. Debates about the origin of C. pepo have been on-going since at least 1857. There have traditionally been two opposing theories about its origin: 1) that it is a direct descendant of C. texana and 2) that C. texana is merely feral C. pepo. A more recent theory by botanist Thomas Andres in 1987 is that descendants of C. fraterna hybridized with C. texana, resulting in two distinct domestication events in two different areas: one in Mexico and one in the eastern United States, with C. fraterna and C. texana, respectively, as the ancestral species. C. pepo may have appeared in the Old World before moving from Mexico into South America. It is found from sea level to slightly above 2,000 meters (6,600 ft). Leaves have 3–5 lobes and are 20–35 centimeters (8–14 in) wide. All the subspecies, varieties, and cultivars are interfertile. In 1986 Paris proposed a revised taxonomy of the edible cultivated C. pepo based primarily on the shape of the fruit, with eight groups . All but a few C. pepo cultivars can be included in these groups. There is one non-edible cultivated variety: C. pepo var. ovifera.

A classification of cultivated C. pepo varieties based on Paris' eight groups and the one non-edible variety
Cultivar group Botanical name Image Description
Acorn C. pepo var. turbinata Green acorn squashes Winter squash, both a shrubby and creeping plant, obovoid or conical shape, pointed at the apex and with longitudinal grooves, thus resembling a spinning top, ex: Acorn squash
Cocozzelle C. pepo var. Ionga Slender green Cocozzelle squash Summer squash, long round slender fruit that is slightly bulbous at the apex, similar to fastigata, ex: Cocozelle von tripolis
Crookneck C. pepo var. torticollia (also torticollis) Yellow curved squash Summer squash, shrubby plant, with yellow, golden, or white fruit which is long and curved at the end and generally has a verrucose (wart-covered) rind, ex: Crookneck squash
Pumpkin C. pepo var. pepo
Round orange pumpkin
Winter squash, creeping plant, round, oblate, or oval shape and round or flat on the ends, ex: Pumpkin; includes C. pepo subsp. pepo var. styriaca, used for Styrian pumpkin seed oil
Scallop C. pepo var. clypeata; called C. melopepo by Linnaeus Whitish round squash Summer squash, prefers half-shrubby habitat, flattened or slightly discoidal shape, with undulations or equatorial edges, ex: Pattypan squash
Straightneck C. pepo var. recticollis Yellow straight squashes Summer squash, shrubby plant, with yellow or golden fruit and verrucose rind, similar to var. torticollia but a stem end that narrows, ex: Straightneck squash
Vegetable marrow C. pepo var. fastigata White oval squash Summer and winter squashes, creeper traits and a semi-shrub, cream to dark green color, short round fruit with a slightly broad apex, ex: Spaghetti squash (a winter variety)
Zucchini/Courgette C. pepo var. cylindrica Slender green squash Summer squash, presently the most common group of cultivars, origin is recent (19th century), semi-shrubby, cylindrical fruit with a mostly consistent diameter, similar to fastigata, ex: Zucchini
Ornamental gourds C. pepo var. ovifera Squash that is that half yellow and half green Non-edible, field squash closely related to C. texana, vine habitat, thin stems, small leaves, three sub-groups: C. pepo var. ovifera (egg-shaped, pear-shaped), C. pepo var. aurantia (orange color), and C. pepo var. verrucosa (round warty gourds), ornamental gourds found in Texas and called var. texana and ornamental gourds found outside of Texas (Illinois, Missouri, Arkansas, Oklahoma, and Louisiana) are called var. ozarkana.
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