Thalamus of a Flower (Explained with Diagram)

In this article we will discuss about the thalamus of a flower with the help of a diagram.

The short axis that holds the four sets of floral leaves is called the thalamus. It is the swollen end of the peduncle or pedicel, which has four nodes and internodes that are very tightly packed together (Figure 1). The leaves of the flowers stay in place on the nodes in whorls or spirals. In some flowers, where the thalamus is very long and the internodes are clear, it is easy to see that the thalamus is an axis.

Anthophore, androphore, and gynophore are the names of the internodes that connect the calyx and corolla, the corolla and androecium, and the gynoecium and gynoecium, respectively (Figure 2). Passion-flower has a distinct androphore, and Pterospermum has a gynophore (B. Kanak champa). Gynandrophore, also known as the androphore-gynophore complex, forms in Gynandropsis (B. Hurhure).

Thalamus of a Flower

Figure 1: A flower of Capparis showing gynophore; B flower of Gynandropsis showing androphore and gynophore.

The thalamus can be cup-shaped in roses, slightly elongated in Michelia (B. Champaka), convex in Datura and China roses, and flat on top like a lotus. Flowers can be hypogynous, perigynous, or epigynous depending on the thalamus’ structure and how the first three floral sets are inserted into the gynoecium.

Thalamus of a Flower

The thalamus of a hypogynous flower is convex and dome-shaped, and the pistil occupies the top position of the thalamus, with the other whorls staying inserted below the pistil one after the other in normal order. The ovary is referred to as superior in this situation. Datura, for example.

Perigynous flowers have concave or cup-shaped thalamus that forms rims or flanges around which stamens, petals, and sepals are arranged. The ovary is regarded as inferior.

Examples: peas and roses. The epigynous flower has a hollow and cup-shaped thalamus that entirely unites with the lower half of the pistil (ovary). Above the pistil are the stamens, petals, and sepals. In an epigynous flower, the ovary is inferior. Sunflower, Cucurbita (B. Gourd), and tube-rose are other examples.

Flower = shoot

The flower is said to be the equal of a shoot. The following facts can be used to back up the preceding statement. Floral buds, like leaf buds, form in either the terminal or axillary position. The floral members persist on the thalamus in whorls or spirals similar to leaf phyllotaxy.

The arrangement of floral elements in relation to one another (aestivation) is analogous to the arrangement of leaves in the bud stage. Floral buds are converted into bulbils (swollen bodies for vegetative growth) in plants such as Aloe and Pineapple.

The thalamus is normally a short, shortened axis with suppressed nodes and internodes. The thalamus’s axis-nature is visible in flowers such as Pterospermum, passion-flower, Gynandropsis, and others, where the internodes between the whorls are quite distinct.

A unusual feature present in some roses and pears is that the thalamus extends or prolongs past the flower and bears normal leaves instead of terminating at the flower. This situation, known as ‘monstrous development,’ demonstrates the thalamus’s axis-nature even further.

Thalamus of a Flower

The leaf nature of the members of the accessory whorls sepals and petals is quite obvious, given that they are usually enlarged bodies that resemble foliage leaves in form and venation.

One spreads out like a leaf in Mussaenda (Figure 3). The main issue emerges in the case of the essential mem­bers stamens and carpels. In water-lily, the slow transition from one member to another sepals to petals, petals to stamens is noticeable (Figure 4).

Of many cultivated flowers, the floral leaves in water-lily, stamens are observed to be changed into petals, a phenomenon known as ‘flower doubling.’ Examples include rose, China-rose, and Hibiscus mutabilis. Canna, a common garden flower, has petaloid stamens and styles. All of this evidences that the stamens and carpels are morphologically comparable to the leaves.