Phaseolus acutifolius var. acutifolius

A.Gray

Sharpleaf Tepary Bean

Fabaceae Potential hazards — see below

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esophiea

gbif· cc-by-nc

esophiea

gbif· cc-by-nc

esophiea

Description

Phaseolus acutifolius var. acutifolius is a ANNUAL CLIMBER growing to 2 m (6ft) by 1 m (3ft 3in) at a fast rate. See above for USDA hardiness. It is hardy to UK zone 9 and is not frost tender. The flowers are pollinated by Insects. It is noted for attracting wildlife. Suitable for: light (sandy), medium (loamy) and heavy (clay) soils, prefers well-drained soil and can grow in nutritionally poor soil. Suitable pH: mildly acid, neutral and basic (mildly alkaline) soils. It cannot grow in the shade. It prefers dry or moist soil and can tolerate drought.

Edible Uses

Mature seeds - dried. They are used as dry shell beans to make soups. They are also ground into flour, fried, parched, or processed into a meal for commercial use. Tepary beans have a strong flavour and odour and are less palatable than common beans. The seedpods are 40 - 100mm long, 5 - 13mm wide and 4 - 8mm thick, containing 2 - 9 oblong to rounded seeds 4 - 10mm long, 4 - 7mm wide and 2 - 5mm thick. On storage, the dry seeds become very hard and take a very long time to cook. Cultivars with white seeds have a more permeable seed coat than cultivars with black seeds, resulting in a shorter cooking time. The young, green seedpods are occasionally eaten. The seeds can be sprouted and then eaten cooked or in salads. The leaves are considered edible in parts of Africa, but they are tougher than those of the common bean (Phaseolus vulgaris) and take longer to cook. The mature seeds (beans) are edible, but only when thoroughly boiled. Raw or undercooked beans are highly toxic, containing lectins, trypsin inhibitors, phytates, and other anti-nutritive compounds. Boiling neutralizes these hazards and makes the beans safe to eat. Tepary beans were an important traditional food of Native Americans in the Southwest. They thrive in the desert, sprouting after rainstorms and producing crops quickly—often in just two months. Domestication traces back over 2,000 years to the Tehuacan Valley of Mexico. The beans come in a variety of colors and are generally larger and more flavorful than most other wild southwestern beans. Their taste, texture, and aroma are very similar to cultivated beans, without harsh flavors. Immature pods are green and soft, while mature pods are brittle and often hairy, releasing beans explosively when ripe. Gathering requires care, since pods can split and scatter seeds. Nutritional & Foraging Notes: Beans mature from early to mid-autumn. Foragers may collect them directly from pods or from the ground after pods burst. Seeds winnow easily and require little processing beyond boiling.

Known Hazards

The seed contains various antinutritional factors, such as trypsin inhibitors, flatulent oligosaccharides and phytic acid. The lectin activity is exceptionally high, but is readily reduced by cooking; whereas cyanogenic glucosides have not been detected. Consumption of raw tepary bean flour has been recorded to cause death in mice and rats within 3 - 4 days, but soaking and cooking the seeds eliminated toxicity completely.

Distribution

Central America - Guatemala; Southwest N. America - southern Mexico north to Arizona, New Mexico and Texas.

Where It Grows

Native to: Arizona, Mexico Northeast, Mexico Northwest, Mexico Southwest, New Mexico, Texas. Introduced into: Canary Is., Central European Rus, India, Kazakhstan, Kirgizstan, Krym, Mali, South European Russi, Ukraine.

Cultivation

Phaseolus acutifolius is a plant mainly of the drier subtropics, though it can also be cultivated in warmer regions of the temperate zone so long as there is a sufficiently long growing season to ripen the crops in autumn. It can also be grown in tropical areas at elevations up to 1,900 metres so long as the climate is not excessively wet. It prefers a mean annual temperature within 20 - 30°c but can tolerate 8 - 38°c. It cannot be grown at night temperatures below 8°c. It prefers a mean annual rainfall of 600 - 1,000mm, tolerating 300 - 1,700mm. Excessive rainfall may create vegetative growth at the expense of seed yield. The plant can withstand heat and a dry atmosphere, though only very few varieties are suited for the wet tropics. Requires a sunny position. Succeeds in most soils that are well-drained. Succeeds in poor, shallow soils. Established plants are rather drought resistant. It prefers a pH range of 6 - 7 but tolerates 5 - 8. The crop can be grown on residual soil moisture. Often cultivated for their edible seed, there are many cultivated forms with seeds considerably larger than the wild forms. The seedpods of wild forms have pods that burst open explosively when ripe to expel the seeds, which are smaller than cultivated forms. The seedpods of cultivated forms remain closed when the seeds first ripen, making harvesting much simpler. The species is highly length sensitive, growing under natural field conditions during the long summer days and beginning to bloom in late summer when day length has fallen to around 13 hours. Flowering occurs within 27 - 40 days from germination. First harvest may take as few as 60 days in the tropics, though in cooler climates, it can be up to 120 days from sowing. The seeds of many domesticated types of tepary beans are shattered less easily than those of wild types. Average yields of dry seed under dry conditions are reported to be 450 - 800 kg/ha and, with irrigation, 0.9-1.7 t/ha. In areas of poor rainfall, tepary bean has possibilities as a catch-crop where a rapid food supply is needed. This species has a symbiotic relationship with certain soil bacteria; these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant, but some can also be used by other plants growing nearby. USDA Hardiness Zone: 8–11. Weed Potential: Low. This is not considered invasive; instead, it is a drought-hardy native adapted to desert soils.

Propagation

The seed of cultivated forms absorbs water easily; in moist soils, the testa wrinkles within 5 minutes, whilst when soaked in water, the testa wrinkles in 3 minutes. This leads to quick and even germination. The rate of germination increases with increasing temperatures from 10 - 35°c. Seedling emergence is faster in white-seeded than in dark-seeded types. The seed of wild forms usually has a hard seed coat and will benefit from scarification before sowing in order to speed up and improve germination. This can usually be done by pouring a small amount of nearly boiling water on the seeds (being careful not to cook them!) and then soaking them for 12 - 24 hours in warm water. By this time they should have imbibed moisture and swollen - if they have not, then carefully make a nick in the seedcoat (being careful not to damage the embryo) and soak for a further 12 hours before sowing. The seeds of domesticated types have no dormancy, which is a disadvantage in humid regions, where fallen seeds will germinate rapidly.