Canola is a member of the \(Brassica\) family, which includes cabbage and mustard, and is scientifically known as \(Brassica\) \(napus\) or \(Brassica\) \(rapa\). The name “canola” originated as a trademark for varieties of rapeseed bred to contain low levels of erucic acid and glucosinolates. This crop is cultivated primarily for its seeds, which are crushed to produce vegetable oil for cooking and industrial uses, making it one of the world’s largest sources of edible oil. A canola field undergoes a dramatic visual transformation, moving from a subtle carpet of green to a widely recognized burst of brilliant yellow.
The Vegetative Stage Appearance
Before the vibrant yellow flowers emerge, a canola field appears as a dense, bluish-green ground cover. During its earliest stages, the plant develops a rosette structure, where the leaves grow in a circular cluster close to the soil surface. This formation allows the plant to efficiently capture sunlight and store energy before the central stem elongates.
The leaves are distinctive, especially the basal, or lower, leaves, which are large, lobed, and have a waxy coating. This waxy texture gives the foliage a slightly glaucous or bluish-green tint, which helps reduce water loss. As the plant matures and the stem develops, the upper stem leaves become smaller, less lobed, and partially clasp the central stalk.
The stem of the young canola plant is smooth and solid, sometimes exhibiting a slight purplish color near the base. This stem remains relatively short until the plant receives environmental signals that trigger the reproductive phase. The plant’s growing point remains protected during the initial seedling stage, making the rosette appearance the defining characteristic of this pre-flowering period.
The Chronology of Canola Growth
The visual life cycle of canola begins with seedling emergence, where the heart-shaped cotyledon leaves first push through the soil. Following the rosette stage, the plant enters bolting, which is the start of dramatic vertical growth. During bolting, the central stem rapidly elongates, often growing from a few inches to several feet tall within one to two weeks.
After the stem stretches, the green bud stage begins, where small, tight clusters of future flowers become visible but remain enclosed by surrounding leaves. This progresses quickly into the yellow bud stage, where the bright yellow color of the petals begins to show through the sepals. The main stem is now topped with a cluster of buds, signaling the imminent arrival of the bloom.
The flowering stage, or bloom, is when the fields achieve their iconic bright yellow appearance. Individual flowers are small, possessing four petals arranged in a cross shape, characteristic of the \(Brassicaceae\) family. These flowers are borne on indeterminate clusters called racemes, meaning flowering begins at the bottom of the stalk and proceeds upward.
This indeterminate growth allows the canola plant to simultaneously develop pods on the lower stem while new flowers continue to open at the top. Peak bloom, where 50% of the flowers on the main raceme are open, creates the densest yellow color across the field. This vibrant phase typically lasts for two to three weeks before the petals drop, marking the transition to pod development.
As the petals fall, they are replaced by long, narrow seed pods, known as siliques, which are initially a vibrant green color. Siliques are cylindrical, smooth, and measure between 45 to 100 millimeters in length, housing 15 to 30 seeds each. The visual sign of maturation is the shift in pod color, progressing from green to pale yellow, then to a tan or dark brown shade. This color change indicates the seeds inside have reached maturity and are turning dark brown or black, signaling the crop is ready for harvest.
Visual Differences from Similar Crops
Canola is often confused with related crops, primarily different varieties of mustard, but specific visual cues allow for clear distinction in the field. A primary difference is found in the leaves during the vegetative stage. Canola leaves are smooth and hairless or have sparse hairs near the margins, and the upper leaves are sessile, meaning they directly attach to and partially wrap around the stem.
Mustard plants, in contrast, have leaves that are densely covered with small hairs, giving them a pubescent or fuzzy texture. Mustard leaves are light green and do not clasp the main stalk, instead terminating higher up on a distinct leaf stem. This difference in leaf texture and attachment provides an immediate visual identifier before the flowering stage.
Once the flowers appear, the pods, or siliques, offer another reliable distinction in their shape and angle of attachment. Canola siliques are long, smooth, and project almost straight out from the stem at a near 90-degree angle. Many mustard varieties, such as brown mustard, develop pods that are shorter and position themselves at a more acute 45-degree angle to the main stem.