Flower Development and Time
Why does a person who suffers from ragweed pollen allergies only suffer during a specific time in the summer? The answer is that the ragweed plant produces pollen only during flowering and flowering occurs during a limited and specific time of the ragweed plant’s life. While this is a good thing for the ragweed allergy sufferer, the timing of flower development can have an impact on the appeal of a landscape plant or the success of seed production in a crop plant.
We can think of the time-limited aspect of flowering in two ways. First, a plant may have a very specific time period in which it produces flowers or the plant may flower over weeks or months. Second, the development of any individual flower on a plant involves many steps and stages but the period of time in which the anthers are shedding pollen or the stigma and ovaries are receptive to pollen is limited to several hours.
The time period at which a plant will produce flowers is often tied to the plant’s growth pattern and life cycle. For example, many plants produce flowers over a time period that lasts only several days. With perennial plants this is often during the early part of the growing season so the plant has time to produce seeds, the seed can disperse and the seedlings that grow from these seeds can become established. In contrast to this, other plants such as impatiens and beans will produce flowers and bloom over a longer time period. Plants that continue to produce flowers during a growing season are called indeterminant while determinant plants have a more specific period of flowering.
Grain crops that are grasses tend to flower during a short time period. Some grain crops planted in the spring (corn, wheat, barely and oats) will flower by midsummer. In contrast, sorghum and pearl millet flower in late summer. Some soybean varieties will flower continuously for 7 to 11 weeks after emergence.
The development of any given flower on a plant always follows a specific sequence of stages. Early stages allow the stamen and pistil to develop from a series of regulated cell division and cell differentiation steps. These steps occur inside the plant or in an inconspicuous bud. The actual blooming of the flower is the dramatic final chapter in the flower’s life. In a few hours or a couple of days, the sepals and petals will enlarge and open and this is timed with the maturity of the stamen and pistil. Timing and opportunity are critical for reproductive success. When pollen is shed at the same time that the stigmas are ready to receive it, fertilization can occur. Successful sexual reproduction will result in seed development. If the pollen fails to land on a receptive stigma during this critical window of receptivity, no seed will develop.