Wild Plants of Moreton Bay

This month marks the one year anniversary of when I headed out into the bush for the first time to study not animals, but plants. It was a decision that changed my life, and I've since come to enjoy going on tree ID quests as much as I enjoy a bout of birdwatching, snorkeling or spotlighting. 

Last Saturday, I decided to celebrate this momentous occasion with a dawn stroll around King Island Conservation Park, off the coast of Wellington Point.
The island is actually connected to the mainland foreshore by a sandbar at low tide, and is an extremely popular walk with the locals. It shrinks in size with every passing decade, as damaged vegetation and increasing storm erosion shepherd it towards an uncertain fate. Historically, the island existed as a coral cay and was known to the local Aboriginal people as 'Yerra-bin'. Living coral species still exist in the water surrounding it, but only just—as our coastal development increases the turbidity of Moreton Bay, these and other marine life forms have begun to perish. 

Though just one hectare in size at high tide, King Island still supports a number of interesting and sometimes quite uncommon plant species, nine of which are shown here.


Grey Mangrove (Avicennia marina)

Sunrise over the edge of King Island's Grey Mangrove forest.

This is South-east Queensland's most common mangrove species, and also the one that dominates the margins of King Island. Mangroves are a group of unrelated trees that have evolved ways to tolerate tidal inundation; this species' method is to increase its oxygen intake by sending aerial roots to the surface, that protrude like little fingers above the mud. These are called 'pneumatophores' and are a distinctive feature of our local mangrove forests. This habitat becomes a marine jungle at high tide and is a breeding ground for the fish and crustaceans that end up on our dinner tables later on. Aborigines and early European settlers both found that the timber of this tree was light and strong, and was thus suited for the construction of canoes, paddles and boats.  


Coastal She-Oak (Casuarina equisetifolia)

Thanks to their drooping, filamentous foliage, Coastal She-Oaks are also known as 'Horsetails'.

Apart from maybe the Pandanus (Pandanus tectorius)—which also grows on King Island—I can't think of another tree more iconic of our Queensland beaches than the She-Oak. Listening to the sound of the crashing surf as the wind whistles through the fine branches of this tree is one of life's simple pleasures, especially on a hot day after a refreshing swim. The Coastal She-Oak is usually the first tree to be encountered in the dunes, as it can tolerate a lack of soil nutrition by drawing upon atmospheric nitrogen instead. Occasionally, it becomes so successful that it forms dense, pure stands that exclude other species; this fortunately hasn't happened on King Island, where it exists alongside a variety of other trees.


European Sea Rocket (Cakile maritima)

European Sea Rocket

Brightening up the dunes with its little white petals, the Sea Rocket is a distinctive plant of King Island, despite its small size. As its name suggests, it is unfortunately not a native species, having been introduced from its homelands in Europe, North Africa and the Middle East. 

A number of other exotic weeds thrive in the Conservation Park also. Once upon a time, a dense colony of Prickly Pear (Opuntia stricta) overran the island and had to be eradicated; a few small specimens still survive. Cobbler's Pegs (Bidens pilosa) throw up their little white flowers and sticky seed heads all throughout the undergrowth, which increasingly consists of introduced Passionfruit (Passiflora sp) in some areas. In the centre of the island exists a beautiful but potentially invasive Brazilian Cherry (Eugenia uniflora). 


Orange Mangrove (Bruguiera gymnorrhiza)

Red Mangrove stilt roots; INSET: leaves.

At first glance, this mangrove can almost look like a lush rainforest fig growing by the sea. On King Island, it is found in the interior landward side of the mangrove forest.

The aerial roots of the Orange Mangrove look like little chunky knees or elbows sticking up out of the mud, and the base of the tree has buttress roots also, just like a rainforest tree.

Orange Mangrove seeds are about twenty centimeters long, and look like floating green sticks with a swollen end. This thicker section absorbs water until it sinks, swinging the seed to a vertical position so that it can catch on the sand and take root. In contrast, Grey Mangrove seeds are fleshy lime-green capsules the size of a walnut, but more flattened.

Originally, I had mistakenly considered this tree to be a Red Mangrove (Rhizophora stylosa).


Cotton Tree (Hibiscus tiliaceus)

Cotton Tree

Growing behind the mangroves on King Island is the familiar Cotton Tree. A member of the Hibiscus family, the Cotton Tree produces lovely yellow flowers in the summer, decorating Moreton Bay shores just in time for the Christmas school holidays. These flowers, as well as the roots, bark and leaves, are used for medicinal purposes among the traditional landowners of the Pacific region. Local Aboriginal people are known to have created healing infusions from the inner bark of this tree, using it as an antiseptic on open wounds. 

The leaves of the Cotton Tree will often seem half-eaten and full of holes. The culprit is one of the most beautiful creatures in the world—the Hibiscus Harlequin Bug (Tectocoris diophthalmus). Next time you pass by one of these trees, stop for a closer look and see if you can spot some little gems hiding among the leaves.


Coastal Vitex (Vitex trifolia)

The Coastal Vitex is found on seashores from East Africa to Tahiti.

Listed by my field guide as quite an uncommon tree in South-east Queensland, the Vitex nevertheless occurs abundantly on King Island. Identifying it posed quite the headache though, as this large shrub is described in all available literature as being three-leaved (hence the scientific name trifolia), yet some of the foliage on these specimens had five-leaved whorl arrangements. Other parts of the tree—including parts of the foliage that were indeed three-leaved—matched perfectly, so I'd say it's simply a case of this plant not having read the field guide correctly! 


Queensland Ebony (Diospyros geminata)

Queensland Ebony leaf and fruit detail; INSET: tree form

Another uncommon tree, the Queensland Ebony is a dry rainforest species that also adapts nicely to a coastal lifestyle. There is just the one specimen on King Island, right in the centre and next to a track that passes beneath it. Close inspection will reveal blunt, opposite leaves and little pairs of yellow fruit growing along the branches. Once upon a time, the island would have been home to a more diverse mix of coastal rainforest species, but as the years go by, just the Ebony remains.


Sea Purslane (Sesuvium portulacastrum)

Sea Purslane

By far the most numerous plant growing on the sandy foredunes of King Island is the Sea Purslane. It is easily recognised by its dark green fleshy leaves and reddish stems, but its tiny pink flowers are worth a closer look too.

Growing along much of the world's coastline, in times past this plant was a welcome sight to sailors, who would consume it to ward off scurvy. Even in the present day, its high vitamin-C content and salty taste ensures that it is sometimes added to more adventurous salads.

Saltwater Couch (Sporobolus virginicus), New Zealand Spinach (Tetragonia tetragonioides) and the purple-flowered Coastal Jack Bean (Canavalia rosea) vine all grow alongside the Sea Purslane on King Island's dunes. 


Dugong Grass (Halophila ovalis)

Dugong Grass is recognisable by its oval-shaped leaves.

It's not just on King Island itself you can find interesting plant life: the water surrounding it is home to a seagrass meadow. Despite being dominated by the more conventional-looking Eelgrass (Zostera muelleri), patches of Dugong Grass are mixed among this underwater lawn. As its name suggests, the latter species is an essential forage plant for herds of Dugong (Dugong dugon) that roam Moreton Bay, and is also enjoyed by Green Turtles (Chelonia mydas).

Seagrasses provide highly valuable habitat for fish, prawns, crabs and other marine organisms, and help trap sediment and reduce water movement so that the area around them becomes clearer and healthier. Because they are genuine flowering plants, they still require lots of sunlight for photosynthesis, and are easily disturbed by any nearby development that makes the water murkier. People living in the Redlands are extremely lucky to still have such a wonderful marine habitat on their shores, as similar seagrass meadows to the north of the Brisbane River, in places like Sandgate and Redcliffe, have been lost over the decades and won't be returning anytime soon. For King Island to remain the beautiful place it is, the surrounding coastal environment will need to be managed and looked after carefully.