Orchid Flower Structure

General Floral Structure

• Orchid flowers are bilaterally symmetrical, meaning that they can be divided vertically into two symmetrical halves. Flower parts exist in multiples of three, with three sepals, three petals and a tripartite ovary. The orchid flower is attached to the main inflorescence stem by a short stalk known as the pedicel.

Sepals and Petals

• The floral parts of the orchid are located at the apex of the ovary. The three outer segments of the flower are known as sepals. The uppermost sepal is recognized as the dorsal sepal and is the largest of the three. The other two sepals are equally sized, located on either side of the flower toward the base, and are known as the lateral sepals. Of the three petals, the two upper petals are equal in size and positioned on either side of the flower toward the top or middle. The lower petal, also known as the lip or labellum, is the showiest part of the flower. It varies in shape, size and pattern between orchids and is designed to attract and accommodate pollinating insects.

Fused Sex Organ

• The vast majority of plant families have separate male and female sex organs, but orchids feature male stamens and the female style fused together to form a single reproductive structure known as the column. Most orchids feature a single anther at the top of the column. The pollen of an orchid is packed in waxy mass known as a pollinium, separated from the stigma, or female pollen receptacle, by a tissue flap known as a rostellum.

Resupination

• The flowers of many species of orchids undergo a fairly unique process known as resupination. While the orchid flower is developing, the labellum lies facing the stem. However, shortly before the flower opens, the pedicel twists 180 degrees, rotating the the flower so that the labellum is then at the bottom of the flower.

Inflorescence

• Orchids present flowers in a variety of ways -- even members of the same genus can carry flowers differently. Some orchids have inflorescences of two or more flowers on the end of the floral stalk, or peduncle. The flowering part of the stalk is referred to as the rhachis. Some orchids feature flowers arranged in a spiral attached by the pedical to an erect, unbranched raceme. Many species simply produce one flower at a time.