2. Maca Description

Habit: Lepidium meyenii Walp. is an herbaceous, low-growing, rosette-like plant of frilly leaves with an enlarged tuberous, fleshy underground organ formed by the taproot and the lower part of the hypocotyl (Leon 1964; Tello et al. 1992). These parts of the plant swell during growth, forming a storage organ resembling a turnip.

Lepidium meyenii Walp. is an annual, biennial or perennial plant (authorities do not agree), growing 10 cm to 20 cm in height. Its main stem grows underground, and is 3 cm to 5 cm in diameter at the most wide part and 15 cm in circumference. The secondary stems are decumbent.

Some authorities consider Lepidium meyenii Walp. an annual crop completing its life cycle within a year when climatic conditions are favourable (Quirós et al. 1996). However, often Lepidium meyenii Walp. is considered a biennial plant (Tello et al. 1992) because it has a vegetative cycle followed by a reproductive phase. Furthermore, in the Junín area Lepidium meyenii Walp. is grown as a biennial by holding the hypocotyl/root underground during the dry season. However, during favourable years, when there is enough moisture in the soil and an absence of killing frosts, plants left in the field complete their life cycle within a year. The vegetative phase includes the expansion and growth of the hypocotyl/root and root. These organs are fully enlarged approximately 7 months after planting. At this time the plants initiate their reproductive phase.

The root is succulent and tuberous, although it is not a tuber nor a bulb. It presents numerous lateral roots that are very thin and white-colored, and extend up to 15 cm long. Actually, the main stem is very reduced, almost imperceptible, and the tuberous part is the fusion of the hypocotyl and the upper part of the main root.

This structure, commonly named ‘tuber’, ‘root’, ‘hypocotyl’, ‘fruit’, or simply ‘maca’ is the economic product of Lepidium meyenii Walp. It is hard in consistency and can occur in a variety of colors: yellow, cream, white, reddish, red, light-lead grey, lead grey, black, yellow/purple, white/purple and purple. This is the edible part of the plant and varies between 2 cm and 5 cm in size.

During flowering, at the base of the plant, radially and under the leaves, generative shoots will rapidly grow, producing secondary branches. These will generate most of the seed of the plant. Approximately 20 primary generative branches are produced per plant, and each of these will produce approximately 13 secondary branches (Aliaga-Cárdenas 1995).

Leaves: The foliage forms a mat, growing in close contact with the ground. The leaves are rosulate, pinnatipartite and are continuously renewed from the centre of the rosette. They are also caulescent, reduced, alternate, and separate. They are fairly polymorphic, according to the position they occupy on the branches or secondary stems. The basal leaves are 5 cm in length, petiolated and bipinnatifid. The central leaves are 3 cm in length and are bipinnatifid. The apical leaves are slightly divided, and 1 cm to 2 cm in length. According to some authorities, the leaves exhibit dimorphism, being larger in the vegetative phase and reduced in the reproductive cycle (Tello et al. 1992).

Flowers: Inconspicuous and arranged in axillary racemes. Often the first floral buds will appear in a small cluster at the centre of the rosette, or as solitary flowers in some of the leaf axils, announcing the initiation of the generative shoots, the main reproductive structures. Only a few of the first flowers will produce fruit. The later flowers are disposed in a simple cluster or raceme. The generative branches will produce profuse flowering racemes which are pauciflorous, short, apical and axillary. There are also axillary flowers that do not form cluster.

The flower is tiny, complete and hypogyne. They have four erect, concave sepals, and four small white petals. The ovary is oval and bicarpelar with a short style, which develops into a dehiscent silicule of two locules, carrying one seed per locule. Only two stamens, or seldom three, with well-developed anthers are present in the flowers. A variable number of rudimentary stamens consisting only of filaments is also present.

The normal number of functional stamens in the family Brassicaceae is six, four larger than the other two. However, androeceum variation reflected in number of complete stamens is a common feature of the genus Lepidium (Thellung 1906). Small nectaries at the base of the stamens are also present. It is unknown, however, whether these are functional.

Aliaga-Cárdenas (1995) found that Lepidium meyenii Walp. is primarily an autogamous species. Pollination is initiated 4-5 days after the flower bud is first visible to the naked eye, and continues for another 3 days. The anthers and petals wither for the next 2 days while the ovary starts to enlarge initiating fruit development. Part of the anthesis takes place while the flower is still closed, thus indicating that the Lepidium meyenii Walp. flowers are partially cleistogamous. Further evidence of autogamy is provided by spontaneous fruit-setting of flowering plants in growth chambers, where insects were excluded (Quirós et al. 1996). In Junín, the native area of Lepidium meyenii Walp. production, no insect pollinators working the flowers were observed. Only sporadic visitation by two or three species of Dipterae which landed in the leaves and flowers has been seen.

In the field at Davis, California, only a few syrphid flies were observed visiting the foliage and seldom the flowers. Plants grown from different accessions are morphologically alike, with a few exceptions. All these observations suggest that Lepidium meyenii Walp. reproduces predominantly by self-pollination.Flowering lasts for three months.

Each secondary branch will yield racemes with 50-70 flowers each. Therefore, a primary branch will bear close to 1,000 flowers. Most of the pollen collected from the flowers is fertile, as measured by pollen stainability. Consistent with other cruciferous species, pollen grains are trinucleated.

Fruit: Silicule (short silique). Fruits will set in most of the flowers throughout flowering time, maturing in approximately 5 weeks. The fruit is dry, slightly marginated at the apex, from 3 mm to 5 mm long and 2.5 mm wide. It possesses two carinated valves, each containing only one seed in each cell. The fruit is longitudinally dehiscent, along the direction of the partition wall, which is membranous. When mature (that is, approximately 5 weeks after fecundation), the fruits will initiate dehiscence; then, the dry pericarp separates in 3 parts and the central, persistent part maintain the seeds linked until they are released.

During the long period of flowering, it is possible to observe both fruits and flowers in the generative branches. Approximately 85% of the fruits will bear seeds. The seeds are small, ovoid, measuring 2 mm to 2.5 mm in length and reddish grey or tan to brown in color, and light in weight (Aliaga-Cárdenas 1995). Apparently seeds do not have dormancy, germinating in 5-7 days at 25°C and good moisture conditions. A single plant of Lepidium meyenii Walp. produces approximately 14 g of seeds. One gram contains approximately 1,600 seeds.

Ploidy: This species is an octoploid with 2n=8x=64 chromosomes (Quirós et al. 1996), considering that the basic genomic number of Lepidieae is x=8. Its meiosis is normal, with the chromosomes associating predominantly as bivalents. This type of association indicates that Lepidium meyenii Walp. is a disomic polyploid. Polyploidy is a common event among the species in the tribe Lepidieae to which Lepidium meyenii Walp. belongs (Darlington and Wylie 1945).