Diversity of flower forms

Human have always enjoyed the beauty and variety of flowers. But flowers serve a specific function for plants - they are the reproductive structures. With over 300,000 species of flowering plants world-wide, plants have evolved all sorts of variations and adaptations for reproducing. The basic parts of a flower are the carpel (female organ), the stamen (male organ), petals and sepals. See here for a diagram of the parts of the flower. Some flowers have both sexes (perfect), some only one (imperfect). Some plants have the sexes on separate flowers, some on separate plants. Some flowers have large beautiful petals, some have none. The variety and combinations is seemingly endless. Here is a small sampling of some interesting flowers one can find on a walk in Central Park.

The Cypress spurge (Euphorbia cyparissias)  seems to have lovely chartreuse petals. However, each tiny flower has no petals or sepals at all. The lime-green structures are bracts, modified leaves sometimes associated with flowers. They serve the same function as petals, that is, to attract pollinators, in this case, bees, flies and ants. Both male and female flowers are found in the inflorescence (cluster of flowers) of this species. We found this stand of spurge in the flower beds at Cherry Hill this summer.

Euphorbia cyparissias Euphorbiaceae

The next flowers shown below are from a Hackberry tree. Hackberries are interesting for many reasons, one reason being that it has three types of flowers - male, female and perfect flowers. The flowers are small and inconspicuous because they are wind pollinated. There is no reason for showy petals or bracts since no pollinators are being attracted. The flowers dangle and let the wind carry the pollen!

Celtis occidentalis Cannabaceae

Everyone knows what violet flowers look like right? Well.... maybe not! The purple and white flowers that violets put out in the spring are what we are used to seeing. But did you know they develop a second set of flowers in the summer that most of us never see? The second set of flowers are called cleistogamous flowers. They produce no petals or sepals. They don't even open, except to eject the ripe seeds. Cleistogamy is an energy efficient way to reproduce (no need to make petals, sepals or nectar). But it means the plant self-fertilizes and there is no genetic variation (except by rare mutation). In the two photos below you can see the small cleistogamous flowers at the base of Viola sororia. Daniel and I found these along the bridle trail on the west side this summer.

Viola sororia Violaceae

Viola sororia Violaceae

This next one is not a flower, but it is an interesting way to reproduce and it occurs on what looks like a flower stalk. Members of the genus Allium (onions and garlic) grow from underground structures called bulbs. One of the ways they reproduce is to produce small new bulbs called bulbils, which are attached to the bulbs and eventually break off and form a new plant. But in some cases they produce the bulbils on flower stalks.  The next two photos below are of a species called Walking onion (Allium x proliferum). The bulbils make the stalk heavy so that it bends to the ground. Once they touch the ground the bulbils germinate into new plants. These are the steps in the onion's "walk".

Allium x proliferum Amaryllidaceae

Allium x proliferum Amaryllidaceae

Wild garlic (Allium vineale) also makes aerial bulbils, and when they are knocked off the flowerhead they can germinate into new plants. In the photo below, the bulbils are germinating while they are still attached to the stalk.

Allium vineale Amaryllidaceae

To see male and female flowers on the same inflorescence, let’s look at Cattails (Typha spp.). This genus produces inflorescences with a huge number of tiny flowers. The top part of the inflorescence is the male flowers and the bottom part, the female flowers. This is another species that is wind pollinated, so there are no petals or sepals present. Each male flower is just a pair of stamens, and the flowers wither once the pollen is shed. The female flowers are equally inconspicuous, but there are so many packed so densely that the structure looks like a sausage (some say corn dog). The second photo below shows where the male and female flowers meet and show some pollen already shedding. 

Typha angustifolia Typhaceae, at the Pond

Typha angustifolia Typhaceae, at the Pond

Orchids are a favorite flower of many people, and with this family being one of the two largest families of flowering plants, there are lots of orchids from which to choose! In Hallett, there is a small stand of Yellow lady's slipper orchids (Cyprepedium pubescens) that the Conservancy planted. Orchids are pollinated by insects so they do produce showy petals and sepals, three of each. The lower petal is shaped like a slipper or a pouch and the two lateral petals are twisted and hang along side the pouch. Two of the three sepals are fused together, this and the third one form a hood above and below the petals. The flower is showy so pollinators come thinking they will find nectar, but they are fooled! There is no reward for pollinating this plant. They get stuck in the slipper and get pollen dusted on them as they are trying to figure out how to get out. Once they do, they are often fooled again and pollinate the next flower in which they are unlucky enough to get stuck.

There are so many more examples of strange and wonderful flowers. All one has to do is look closely, so keep your eyes open when enjoying your walk though Central Park!

Cyprepedium pubescens Orchidaceae