Alfalfa (lucerne) is a globally cultivated perennial legume prized for its high protein content and ability to enrich soil nitrogen. While the standard, most widely grown commercial variety displays a vibrant purple hue, the question of whether this forage crop produces yellow flowers has a nuanced answer rooted in botany and breeding history. Distinct species and hybrid forms of alfalfa do feature yellow blossoms. Understanding these color differences is fundamental for identifying alfalfa strains and appreciating the plant’s genetic diversity.
The Predominant Flower Color of Alfalfa
The alfalfa most commonly planted globally is Medicago sativa, characterized by flowers in shades of violet and deep purple. This color is the baseline expectation for commercial varieties, derived from anthocyanin pigments in the petals. The flowers are small, typically measuring less than half an inch, and are structurally similar to those of a pea plant.
These small, pea-like flowers are grouped in dense, short clusters called racemes, which emerge from the leaf axils. Each individual flower has a distinctive papilionaceous shape, consisting of an upright banner petal, two lateral wing petals, and a fused keel petal enclosing the reproductive organs.
Identifying Yellow-Flowered Varieties
Alfalfa does have yellow-flowered relatives, most notably Medicago falcata, often called Yellow Lucerne or Sickle Medick. This species naturally produces blossoms colored by xanthophyll and carotene pigments instead of anthocyanins. The yellow flowers tend to be slightly smaller than the purple variety, ranging from light yellow to a darker orange-yellow.
M. falcata is recognized botanically as a subspecies of common alfalfa (Medicago sativa ssp. falcata). Significant populations of yellow-flowered alfalfa are found in the hybrid known as sand lucerne (M. sativa ssp. varia), which results from a natural cross between the purple and yellow species. This hybrid displays a wide spectrum of flower colors, including pure yellow, purple, and variegated forms.
Yellow-flowered alfalfa exhibits several traits that distinguish it from the standard purple kind beyond mere color. M. falcata possesses a greater tolerance for cold and frosty conditions, making it suitable for harsher northern climates. It also develops a more fibrous, creeping root system, which contrasts with the single, deep taproot characteristic of purple M. sativa. The seed pod is another key identifier: the yellow variety produces curved, sickle-shaped (falcate) pods, while the purple variety’s pods are coiled in two to three tight spirals.
The Practical Significance of Alfalfa Flower Color
The color of an alfalfa flower serves as an important marker for breeders and farmers. Since flower color is genetically controlled, plant breeders use it as a trait to track and identify specific genetic material during selection programs. Distinct flower colors can quickly signal the genetic background of a variety, aiding in the development of new strains.
For growers, the color is a reliable indicator of seed purity and the presence of contamination. A field planted with a pure purple variety should not exhibit a significant number of yellow or variegated flowers. The unexpected appearance of yellow blossoms suggests the presence of M. falcata or its hybrids, indicating potential cross-pollination or the introduction of an unwanted species. This visual cue helps farmers and seed producers verify the integrity of their crop.