The arrangement of flowers on a plant follows specific patterns known as inflorescences. This floral architecture plays a significant role in reproductive success and attraction of pollinators. The flower spike is a structure that lends a vertical presence to the landscape. It is a dense column of blooms rising from the foliage, representing a fundamental design in plant biology.
Defining the Spike Inflorescence
A flower spike is botanically classified as a simple, unbranched, indeterminate inflorescence. The core structure is a single, elongated central stalk, termed the rachis. The rachis continues to grow from the top, meaning flowers at the base mature and open first, while the newest buds form near the tip.
The defining characteristic of a true spike is how individual flowers are attached to this central axis. Each flower, or floret, is sessile, meaning it lacks a small, separate stalk, or pedicel. Sessile flowers are seated directly on the main stem, creating the dense, uniform column shape recognizable as a spike.
Distinguishing Spikes from Similar Inflorescences
The spike is frequently confused with the raceme, which is a very similar elongated, unbranched inflorescence. The difference between the two structures lies entirely in the presence or absence of the pedicel, the small stalk holding the individual flower. In a true spike, sessile flowers attach without a stalk, creating a seamless connection to the rachis.
In contrast, raceme flowers are attached to the main axis by distinct pedicels of roughly equal length. Other similar structures include the catkin, which is a modified, often drooping spike that typically bears small, unisexual flowers relying on wind for pollination. The corymb is a flat-topped flower cluster where lower flowers have longer pedicels than upper ones, creating a level surface visually distinct from the vertical spike.
Common Plant Examples and Horticultural Considerations
Many common garden plants showcase the spike inflorescence. True botanical spikes are found in plants like Plantain (Plantago) and the grain crops of wheat and barley. In the ornamental garden, the striking flower stalks of Gladiolus and the purple columns of many Lavandula varieties are often described as spikes due to their tall, dense form.
Understanding the spike structure has practical implications for plant maintenance. Since the flowers open from the bottom up, a common gardening task is deadheading, which involves removing the spent spike once most flowers have faded. This encourages the plant to direct energy into new growth and potentially produce more bloom spikes instead of setting seed. Furthermore, the tall, slender nature of many spikes, such as those on delphiniums or foxgloves, may require staking to provide support and prevent wind damage.