Is lotus different from water-lily?

Who hasn't seen a pond filled with water lilies or lotuses and sighed with content? These beautiful aquatic nymphs with their graceful forms, can fill anyone with serenity. But do you know that a lotus is very different from a water lily? Looking at a flower or a plant in a pond, can you tell which one is a lotus and which one, a lily? In fact, the differences between the two are more than what one would imagine.

Water lily is a common name for a group of aquatic flowering plants belonging to family Nympheaceae whereas Lotus, scientifically known as Nelumbo belongs to the family Nelumbonaceae. The genus Nelumbo contains only two species, namely, Nelumbo lutea and Nelumbo nucifera. On the other hand, water lilies, placed in the genus Nymphaea include about 70 species.

The most striking difference between lotus (Nelumbo) and a water-lily (Nymphaea) is in the female part (carpel) of the two. The lotus flower shows a barrel shaped carpel (ascidiate) that is embedded in an expanded receptacle. If you look closely at the cross section of the lotus, you can also see an androecial ring (a ring formed by the stamens at the base) which is a distinguishing feature for lotus; also tamens of lotus are filamentous unlike the leaf-like (laminar) stamens of the water-lily. Of course, the most commonly cited difference and the one which will help you decide which plant it is from a distance, lies in the leaves of the two plants. The leaves of lotus are emergent, meaning that they rise above the water level whereas the leaves of water-lily are found floating on the water surface. Same is true for their respective flowers; lotus flowers are emergent and water-lily flowers are floating.

For a long time, there was a confusion amongst taxonomists regarding the relationship of lotus (Nelumbo) and water-lily (Nymphaea). No wonder!! When the experts don't agree on it, how is a layperson to decide? But using DNA evidence along with other taxonomic studies, researchers now agree that lotus and water-lily belong to two different families. In fact, studies have shown that whereas lotus is a member of the more evolved group of plants known as the 'Eudicots', water-lily is a member of a primitive group (Nympheales) that occurred as early as the cretaceous period. The lotus plant is more closely related to Platanus or the sycamore also known as the plane tree and the members of the family Proteaceae!! A closer look by botanists reveled many similar features in the floral and vegetative morphologies between the members of lotus, sycamore and proteas.

Platanus and Lotus
Figure 2: Sycamore, Lotus
The water-lilies are now considered to provide the critical missing link in the evolution of flowering plants. Fossil records and molecular studies have shown water lilies to be amongst the earliest flowering plants. Studies on the development of endosperm in Nuphar polysepalum (pond lily) have shown that this group of plants lies between the gymnosperms (non-flowering plants) and the angiosperms (flowering plants).

Victoria amazonica is one of the most amazing waterlilies known. It impresses not only by the size of its gigantic leaves which grow up to as much as six feet or the beautiful flowers which may be as large as a foot, but also by the contrivances one observes during pollination.

Figure 3: Leaves, Flower

The flower is pollinated by scarab beetles. As can be seen in the first figure, the pistil of the water-lily lies at the base of a hollow chamber like structure surrounded by the stamens. This hollow chamber hides the reward for the beetles in form of sugar and starches. The flower buds develops under water and when ready to open, they emerge above the water surface between the surrounding leaf pads during day time. However, the buds open only as the sun sets and the white petaled, fragrant flowers draw the beetles. The beetles have to crawl into the inner chamber to get their bounty. As midnight approaches, the flowers start closing in, thereby trapping the insects feasting on them. The closed petals start changing their color from white to pink. Next day, the flowers reopen with a purplish hue, still entrapping the insects from the night before as the tunnel to the inner chamber remains constricted. With sunset, this constriction is removed and the beetles are able to scramble out of the chamber. But as they move through the anther lined tunnel, the pollen from the now open anthers stick to the sugar covered beetles. The beetles carrying pollen from these flowers will fly out to visit the freshly opened, white colored flowers bringing about their cross-pollination. To witness this saga of sweet entrapment, watch a very informative and beautifully shot, short documentary by David Attenborough.

Water lilies and lotuses make beautiful addition to any water garden. I will write more about the gardening aspects of these plants in my next article.