Summer flowers fade and the pace of life in Westborough picks up in September, but a vision of summertime lingers on shallow ponds where native white water-lilies bloom.

Known as fragrant water-lily (Nymphaea odorata) for the sweet scent of its blossoms, this water plant starts to bloom in early summer but can put on its best show in September. A leisurely trip past the lily pads by canoe or kayak is one of the best ways to enjoy this end-of-summer treat.

Fragrant water-lily thrives in slow or still shallow water 6-15 feet deep, so Mill Pond with its maximum depth of 15 feet is a perfect place for it. The flowers and leaves – the lily pads – grow from a root-like underground stem, or rhizome, in the muddy bottom.

In the fall, the flowers and leaves die back but the rhizome survives the winter. Before lush plant growth covers the pond in the spring, you might see tangled balls of rhizome under the surface, looking like root balls.

Ancestors of today’s water-lilies were among the earliest flowering plants, with a long history going back 125 million years to the time of the dinosaurs. Scientists think that water-lilies descended from early land plants and returned to fresh water. Water-lilies are not actually lilies, which are a more recent group of flowering plants.

Why don’t water-lily flowers sink? How do the flowers and lily pads float on a pond? The surface tension of water has something to do with it. Water molecules are attracted to each other and tend to stick together, making a surface where the round, flat lily pads and flowers can float.

Beyond that, the leaves, flowers, and stems of water-lilies are filled with air spaces that help them float. In a similar way, our air-filled lungs help us float in water, especially if we lie flat on our backs or stomachs and spread our weight over more of the surface.

The air spaces also help to keep water-lily plants alive by bringing oxygen down to the rhizome buried in the muddy depths of the pond. They also bring up carbon dioxide and methane (which we know as smelly sewer gas, which forms as plant and animal matter decomposes in the mud).

Thanks to the air spaces, the rhizomes of water-lilies don’t “drown” the way roots of many familiar trees do when they’re flooded, as happens in new beaver ponds. We think of most land plants as having tubes for bringing water up from roots to leaves and for carrying sugary sap from leaves to roots, but water-lilies also have tubes for moving air through the plant.

Water-lily stems have four air channels, which work somewhat like straws (and have actually been used as straws by people). Air enters and exits the water-lily plant through tiny pores on the tops of the leaves. Newer leaves tend to draw fresh air into the plant, and older leaves tend to let out air that comes up from the depths.

As a native plant of eastern North America, fragrant water-lily has lived in our area long enough to develop many relationships with local wildlife. When you look closely at other native plants such as goldenrod and milkweed, you usually find them alive with insects – from visiting bees, flies, ants and butterflies to resident spiders, beetles and caterpillars – and the same goes for fragrant water-lily. It’s as busy as the town square of a bustling community.

The large, 3-5 inch blossoms of fragrant water-lily open in the morning and close in the afternoon. A flower typically lasts 3 days. Its female parts are ready to receive pollen on the first day, and its scent lures many kinds of bees and flies. These visitors usually fall into a pool of sweet fluid at the center of the flower, where pollen from other flowers is washed off the insects. Most visitors escape the pool.

On the second and third days, the pool is gone but the male flower parts produce their own pollen, which sticks to visiting insects. Finally, after the third day, the flower stem coils, pulling the pollinated blossom under water, where the seeds ripen.

The floating lily pads are a haven and food for insects and other creatures. They are round, with a notch where the stem joins the leaf, and can grow to a foot wide. Look closely and you may see – yes, a frog on a lily pad! You might notice a small painted turtle or a dragonfly or damselfly resting there, or a bird hopping from one lily pad to another as it pursues insects.

Holes in lily pads are clues that beetles have been munching them. Some beetles spend their whole lives on water-lily plants. Certain moth caterpillars feed on the lily pads, and lady beetles may eat aphids that suck the plant’s juices. Certain beetles, dragonflies and damselflies lay eggs in the stems.

Lily pads create shade in a sunlit pond, and fish hide under them. Minnows lay eggs there. Snails feast on the underside of lily pads.

Muskrats and beaver eat and store water-lily rhizomes. Porcupines and our white-tailed deer graze on the plants. Wood ducks and ring-necked ducks eat the seeds.

What about humans? We, too, have turned water-lilies into food. People have boiled young leaves and lily buds and served them with butter. They’ve pickled lily buds and roasted the seeds like popcorn or ground them into flour.

Henry Thoreau, famed naturalist, author of Walden and Concord resident in the mid-1800s, even smoked leaves of fragrant water-lily.

The rhizomes had a role in medicine of old. Native Americans made tea from it to treat lung ailments and intestinal problems such as diarrhea. They mashed it and applied it to swellings and used it to stop bleeding. Later folk medicine mixed the rhizome with lemon juice to remove freckles and pimples.

Fragrant water-lily has been widely cultivated for its beauty and was exported to England as long ago as 1786. It has spread through the western U.S. and Canada.

Yet not everyone is crazy about the plant. In Washington state, it is an invasive plant, choking ponds and interfering with swimming and other recreation. It is listed there as a noxious weed.

More locally, fragrant water-lily on a pond can be a sign that the water has become overly enriched with nitrates and phosphates. These pollutants can come from runoff from heavily fertilized lawns and golf courses or faulty septic systems.