Meet the Scrophulariaceae Family
All species must possess some reliable method of reproducing in order to survive. Several mechanisms occur in the Plant Kingdom for ensuring successful propagation of future generations. Seed production is a primary means of propagation. Morphological characteristics contribute to a plant’s survival success by affecting its pollination efficiency. For example, many members of the Scrophulariaceae (Figwort) family have unique flower characteristics that aid in attracting insects, which serve as the primary pollinators. The corollas are tubular, with flared lips, which serve as inviting 'landing pads' for passing insects. Snapdragons, foxgloves, and penstemons are examples of Figwort family members that exhibit these typical flowers. Throughout this lesson, we will use the genus Penstemon, as an example of the impact a plant’s morphological characteristics play in its ability to reproduce. First, consider the role of the inflorescence, in particular the design of the inflorescence.
The arrangement of individual flowers is an invitation to insects arriving from various directions, and helps assure adequate pollination. Penstemons are very showy when in bloom, and in most species, the inflorescences are held well above the foliage, like a flag waving in the face of oncoming insects. Their flower arrangements vary with the species and can be described in four categories: 1a) spike, 1b) raceme, 1c) thyrse and 1d) panicle .
A spike is tight and narrow, with flowers arising directly from the main stem, or on extremely short pedicels (flower bearing stems). A raceme can be narrow or more open, but the flowers are on longer pedicels. A thyrse, the most common flower arrangement in penstemons, has two secondary stems called cymes at each node of the main inflorescence stem. The two cymes may form a ring around the main stem called a verticillaster, or false whorl. Verticils, which are also called whorls, are clusters of flowers arising at nodes spaced along the stem. Depending on how close together the whorls and false whorls are, the inflorescence can look like a candelabra, or a continuous column of flowers. Sometimes side stems bearing flowers may continue to extend and may be more open and airy. This type of inflorescence is a panicle. Since flower forms have infinite variety, the inflorescence may also fall somewhere between these categories.
The Flower Structure
When looking closely at individual flowers of a plant, identifying characteristics can be seen. For example, all penstemon flowers are tubular corollas, composed of a calyx with five sepals. The corolla throat divides into two lips, the upper with two lobes and the lower with three lobes. A noticeable division into two lips is called biliabate.
Glandular hairs or non-glandular hairs may occur on the corolla. Two pairs of stamens (each with 2 pollen-filled anther sacks) and a staminode are present in this genus. These flower features may be exserted (outside the corolla), included, (the most common condition) or may protrude just to the edge of the throat. The staminode may be glabrous (smooth) or bearded—'beardtongue' is often used as the common name of penstemon.
The staminode characteristics can be important in identification of individual species, but the anthers are usually more important. The pistil is not usually visible until the corolla is removed. As if the broad, colorful throat of the flower were not enough, penstemons often have guidelines, which are directional lines in a contrasting color that lead insects directly to the pistil as you can see in (Fig. 3) below.