Pickerel weed – Pontederia cordata

09 Jul

Summer is here and the temperatures are high. Many plants are dormant in this season: annuals have ended their life-cycle and their seeds are ‘awaiting’ the next rainy season. Bulbs also remain underground, awaiting the rains.

This is the season  for aquatic plants: the plants that grow in streams and ponds, and therefore our plant of the month is a beautiful aquatic plant: Pontederia cordata, or Pickerel Weed (Pontederiaceae).

A lot has been said about the Nymphaea and the Nelumbo that adorn the main lake in the entrance to the garden. But if you look carefully towards the edges of the lake, you will see a clump of tall plants – about 1 to 1.5 meters high, with an elongated narrow purple-blue inflorescence. This is the Pontederia cordata.

The Pontederia originates in the Americas, where it grows in a variety of wetlands, such as streams, ponds, lakes and swamps from Canada in the north to Argentina in the south. In nature, the Pontederia tends to grow in clumps as well.

In order to grow in the water, the plant  must be able to pass oxygen to its roots. The Pontederia has a sponge-like tissue in  its stems, through  which the oxygen moves to the roots. The flowers are small irregular and purple,  with a yellow spot on the upper petal. Each flower is about 1.5 cm long. The flowers grow in a dense spike-like elongated inflorescence on the upper part of the stem. The young leaves are lance-shaped, but become elongated and heart-shaped hence the name ‘cordata’ – heart-shaped.

Many living creatures feed on this plant. Bees and butterflies feed on its nectar. In nature, the Pontederia is pollinated mainly by two rare local  bee species. Deer and rodents eat the leaves. The larvae of some beetles and moths eat the stalks and petioles. Several duck species enjoy the seeds that the plant spreads across the water. Dragonflies and damselflies lay their eggs on the lower parts of the stems,  close to the water. Fish – mainly Pickerels – shelter  among the plant’s roots, hence its common name. All in all, this is a very important plant in the native ecological system in which it grows.

The Pontederia is named after Giulio Pontedera, an 18th century Professor of Botany who was the Director of the Orto Botanico di Padova, The botanical garden of Padua University – founded in 1545,  this is the world’s oldest academic botanical garden that  remained in its original location. Thanks to the commercial connections of the neighboring city of Venice (which ruled Padua for most of the time), many exotic plants were brought to the garden from all over the world, and it became an important center for studying the world’s flora. Pontedera was the director of the garden at  the time of the Swedish Linnaeus, who invented the binomial nomenclature for naming organisms. Pontedera disagreed with Linnaeus’s method, but the two appreciated each other’s work, and kept in touch, which was the reason that Linnaeus named the Pontederia after Giulio Pontedera.

In our garden you can find the Pontederia cordata blooming in several ponds – first, in the large lake in the entrance, but also in the ponds in the America section of the garden. You are invited to tour the garden and look for it!

Author: Yael Orgad, July 2018

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