The severe reduction in our annual rainfall over the last 12 months has resulted in the drying of many waterways, Allen Noble Sanctuary included. This drop in the sanctuary’s water level provided an unexpected opportunity, you could walk across a large section of the Sanctuary without getting your shoes too wet, although I did get wet socks!
Allen Noble Sanctuary, normally under water
The aim of the mornings walk was to closely examine plant species growing in what is normally a wet environment and to discover the type of adaptations they have, which enables survival in an aquatic environment. Such plants are known as hydrophytes.
By examining the internal stem structure of the Tall Rush, Juncus procerus, large air spaces were found which are responsible for moving air from the stems into the submerged plant parts below. This is essential for the Rush’s survival as the saturated soil within the swamp is unable to provide sufficient oxygen for the root’s survival.
Tall Rush
Tall Rush Stem section showing air spaces
Using our magnifying glasses, the succulent stems of Austral Brooklime, Gratiola peruviana, when cut, revealed an amazing ring of cells containing large airspaces connecting leaves and stems above the water with the stems and roots beneath the water.
Austral Brooklime
There was no need for the use of magnifying glasses when examining the internal stem structure of the Tall Spike-sedge, Eleocharis sphacelata, by splitting the stem open we could see very large airspaces creating sections of hollow stems. All designed to allow air to travel to the submerged plant parts, particularly the enlarged horizontal stem known as a rhizome. The rhizome’s purpose is reproduction. As it lengthens, roots and shoots are formed, creating the clumping growth habit of sedges and rushes.
Tall Spike-sedge flowering
Tall Spike-sedge stem section showing very large air spaces
Tall Spike-sedge rhizome
We had an unexpected find whilst we were walking across the spongy surface of the sanctuary. Rather than floating in the water as is the normal growth habit of Pacific Azolla, Azolla rubra, we found it successfully growing as a ground cover.
Pacific Azolla
This aquatic floating fern has breathing pores (stomata) located on the upper surface of its fronds, their purpose enabling air exchange. This is a common adaptation shared by many aquatic plants that have floating leaves. E.g. Running Marsh-flower
Running Marsh-flower (photo by Ellinor Campbell)
As we continued, another surprise was revealed. Normally viewed from a distance, an impressive flower spike of Water Ribbons, Cycnogeton procerum was able to be admired and by feeling the thickened leaf stems we could appreciate the ‘squishy nature’ of the plant cells designed to transport air towards the submerged rhizome and plant roots.
Water Ribbons showing flower spike
A peaceful spot to recap on the mornings observations
Gail Slykhuis (plus all photos except Running Marsh-flower)