Basic Species Information
Horse gram (Macrotyloma uniflorum (Lam.) Verdc. (syn. Dolichos uniflorus Lam.)), also known as kulthi, gahat, Madras gram, grain de cheval, kerdekorn, and favalinha, is a domesticated bean grown today across tropical Africa, South Asia, Southeast Asia, China, and Australia. In much of the older literature on the botany and archaeology of India, it is referred to as Dolichos biflorus, although this is a misnomer, and accepted nomenclature today is Macrotyloma uniflorum (see Smartt 1990; Fuller 2002). The stems and leaves of the plant are often used as fodder, while the beans are harvested for human consumption. Horse gram is tolerant of both drought and low soil fertility, making it a particularly important crop in drier areas of south India (Kachroo & Arif 1970; Smartt 1990). It requires very little input and can be used as a green manure to improve depleted soils. As such, it is often an important component of crop rotation systems in which it is usually planted on fallow fields. It can be successfully intercropped with cereals, including pearl millet, sorghum, and the small millets. In addition, it does well as an understory crop in orchards and plantations.
Horse gram is a drought-resistant crop largely grown in areas with less than 900 mm annual rainfall, though it can be grown with as little as 380 mm. While it can tolerate higher temperatures, ideal temperatures for growth range between 25 °C and 35 °C. As such it is particularly suited to tropical environments. It takes around 120–180 days to reach maturity. Horse gram is easily harvested by uprooting. Because of this a relatively high number of weeds may be incorporated into the crop, increasing the prevalence of weed seeds in assemblages from each stage of processing and potentially increasing the visibility of horse gram crop processing in the archaeological record. It is processed in a similar way to glume-wheats, with two episodes of threshing and winnowing (Fuller & Harvey 2006). The second episode may occur daily, with the day’s quota of the pulse removed from storage and prepared separately. This method increases the chance of archaeological preservation and may bias towards the prevalence of this crop in the archaeological record. The beans are usually dried for storage and longevity. These dry beans tend to be soaked overnight prior to cooking. Boiling is most common; however, they can also be fried or roasted. Boiling produces both cooked beans, which may be fed to humans or livestock, and horse gram water, which can be condensed to produce a thick protein rich stock for soups and broths. In addition, the beans can be sprouted prior to cooking. There are several claimed health benefits and medicinal properties to horse gram, including its diuretic effect which may help kidney stones.
Major Domestication Traits
Timing and Tracking Domestication
The high ubiquity of this crop at Neolithic southern Indian sites c. 2000 BCE suggests that it was a staple food. Furthermore, early finds indicate that it was part of an indigenous south Neolithic crop package along with two millets (Brachiaria ramosa and Setaria verticillata) and another pulse (Vigna radiata) (Fuller et al. 2004). This crop package appears to be synonymous with the semi-pastoral Ashmound culture, in which large areas of accumulated burnt cattle dung and hilltop settlements are prime features. It appears to be a later introduction to the agriculture in the Ganges plains and eastern India (Orissa) in the Chalcolithic after c. 1500 BCE. In the period 400–100 BCE, horse gram is found on the Malay peninsula in southern Thailand, for example, at Khao Sam Kaeo, where it might have been imported with other Indian pulses for Indian enclaves at important craft and trading cities (Castillo & Fuller 2010). Today it is not cultivated for human consumption in Southeast Asia, and this crop has remained restricted to South Asia, mainly as a low-status pulse.