Plant of the month 01/2024: Carallia brachiata

Photo: Julia Hazel

Carallia brachiata is not a rare species in our area but it can be easily overlooked amongst dense creek-bank vegetation. Fortunately it’s often ‘flagged’ by a bright yellow caterpillar poised conspicuously on a dark green leaf (photo above). These distinctive caterpillars of the Four o’clock Moth Dysphania numana rarely feed on other trees, so they are a convenient aid for identifying Carallia brachiata.

During NPQ outings to Cleveland Creek we’ve seen Carallia brachiata (Rhizophoraceae) as a small tree, both along the upstream section of the creek and downstream. However, as its common name Freshwater Mangrove suggests, this species doesn’t extend into the inter-tidal zone. And in less crowded situations, Carallia brachiata grows taller and develops a fine shady canopy like this specimen in Cairns (photo below).

Photo: Russell Cumming

Carallia brachiata has oval leaves that are glossy dark green on the upper side and dull light green underneath (photo below).

Photo: Russell Cumming

Carallia brachiata produces clusters of small greenish-cream flowers (photo below) that develop into globular red fruits (photo second below) relished by many birds.

Photo: Russell Cumming
Photo: Russell Cumming

Plant of the month 10/2023: Crateva religiosa

Photo: John Elliott

Crateva religiosa, an unusual member of the Caper family, is little known in Townsville although a few plant enthusiasts have grown it successfully here. One of our members has a fine specimen doing very well in his garden (photo below) and it is currently in flower (photo above).
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Photo: John Elliott

Crateva religiosa (Capparaceae) grows naturally in Cape York and the Northern Territory and also occurs across Southeast Asia and islands in the Pacific. It has long been considered a sacred tree and planted near temples, as reflected in its species name. In ideal situations it can reach 15 metres but it is much smaller in drier areas. In gardens it can be easily pruned if necessary, as the wood is very soft.

Photo: Russell Cumming

Crateva religiosa may be briefly deciduous at the height of the dry season, before putting out bright green trifoliate leaves and showy delicate flowers in terminal corymbs (photo above). The petals start out white and fade to yellow (photo below).

Photo: Brian Venables

The fruits of Crateva religiosa (photo below) are large with a leathery surface containing numerous seeds in cream flesh. Some people notice a smell of rockmelon on opening these fruits, others find it musky or even nauseating (perhaps depending on the degree of ripening?). The fruits are relished by native mammals and considered edible but not palatable for humans.

Photo courtesy Atlas of Living Australia CC-BY 3.0, for details see:
https://bie.ala.org.au/species/https://id.biodiversity.org.au/taxon/apni/51269947#overview

Plant of the month 09/2023: Dischidia major

Photo: Russell Cumming

Dischidia major (Apocynaceae) is a strange-looking tropical plant, native to Queensland (Cape York) and also occuring in some Asian countries. It naturally grows as an epiphyte, twining around tree trunks and branches, as in the photos above and below.

Photo: Greg Calvert

Dischidia major , sometimes called “Rattle Skulls”, has the unusual habit of bearing two distinct types of leaves at the same time. It has small, almost circular leaves growing in opposite pairs, widely spaced along its twining stems. It also has dense clusters of large, hollow, tongue-shaped leaves.

Photo: Julia Hazel

At our NPQ Townsville meeting this month, we had a close look at a potted Dischidia major grown by one of our members. We discovered each hollow leaf has an almost-hidden entrance at its base, marked by the arrow in the photo above. So what was inside? We cut open a leaf to find out – photo below.

Photo: Greg Calvert

This leaf was empty, except for roots emerging near the petiole and spreading inside the hollow leaf. However, researchers have found wild-growing Dischidia major plants typically have certain species of arboreal ants nesting in their hollow leaves. Apparently the ants benefit from a secure shelter and their waste accumulates inside the leaf together with condensed moisture.

As an epiphyte, Dischidia major does not have the opportunity to absorb nutrients from the earth. However, when it hosts resident ants, their waste creates a small private compost heap in each occupied leaf, from which the plant’s interior roots take up nutrients – a very neat symbiosis!

In cultivation Dischidia major needs very good drainage (a chunky orchid mix is suitable) and intermittent watering. Provided the plant has a sheltered spot with bright indirect light, it grows well in Townsville even though there may be no ants of the right species to occupy its leaves. The plant brought to our meeting even had flowers emerging from its twining stem (photo above, left side above the rim of the pot).

Botanical details are available at https://apps.lucidcentral.org/rainforest/text/entities/dischidia_major.htm

Plant of the month 08/2023: Hakea benthamii

Photo: Greg Calvert

On our August outing to Mt Zero we chose Hakea benthamii as our P o M after finding many specimens, all flowering beautifully and spreading their lovely scent.

Photo: Julia Hazel

Hakea benthamii (Proteaceae) grows as a small-medium shrub (photo above) sometimes up to 4m high. Although its range extends from SE Queensland to near Cooktown, it is sparsely distributed on the coastal ranges and tablelands.

Photo: Greg Calvert

The perfumed flowers are creamy-white with hints of pink, growing in clusters in the leaf axils (photo above).

Photo: Russell Cumming

The fruits are hard woody capsules with an unusual beaked shaped (photo above).

Photo: Russell Cumming

Hakea benthamii was previously called Hakea plurinervia, reflecting the multiple veins in its distinctive leaves (photo above). However, its was subsequently noticed that H. plurinervia had been applied to fossil plants prior to formal description of the living plant, hence the need to change its name (Reference: Ian M. Turner (2014) “Names of Extant Angiosperm Species that are Illegitimate Homonyms of Fossils,” Annales Botanici Fennici 51(5), 305-317)

Plant of the month 07/2023: Cynometra iripa

Photo: Gavin Colthart

Greg brought a specimen of Cynometra iripa to our July meeting, possibly the first-ever mangrove species in our group’s long-running ‘show and tell’ tradition – thank you Greg! And the Cynometra iripa Greg has grown at home (photo below) might be the first ever cultivated in a Townsville garden?

Photo: Greg Calvert

Cynometra iripa (Fabaceae), commonly called Wrinkle-pod Mangrove, has a wide natural range along the coast of Queensland and the Northern Territory, typically growing at the landward side of mangrove forests in places with some freshwater inflow.

Photo: Gavin Colthart

Cynometra iripa is usually a spreading shrub or small tree like this one (photo above) spotted by Claire and Gavin at Magnetic Island, although it has been recorded up to 8 m tall in some places.

Photo: Greg Calvert

Cynometra iripa has compound leaves with two pairs of leaflets (photo above) or sometimes a single pair. Helpful for identification, the central vein of each leaflet is slightly off-centre (photo below).

Photo: Russell Cumming

Attractive clusters of small white flowers produce woody pods (photo below) that have a wrinkly surface as the common name suggests .

Photo: Greg Calvert

At maturity these wrinkly pods are buoyant and their distribution is assisted by water currents. They are sometimes found washed up at the tideline on our local beaches (photo below).

Photo: Russell Cumming

Two other native Cynometra species have been recognised in Australia, including the new species C. roseiflora found only on the Mossman River. For more details see Cooper, W.E. (2015) A taxonomic revision of Cynometra L. (Fabaceae) in Australia, available here.

Native plant notes: What is diallagy?

Most people have seen deciduous trees change colour before dropping their crisp, drying leaves in response to seasonal drought (in our region) or low temperatures (in cold climates) and then grow fresh new leaves when conditions improve.

However, only a few of our group had observed diallagy – or even heard about it – until we went out to White Mountains National Park in noticeably drier conditions than our previous trips.

Photo: John Elliott

‘Diallagy’ describes a remarkable adaptation to survive drought, seen in diverse native plants in Western Australia and a few native species in Queensland. Unlike deciduous leaves, diallagous leaves remain on the plant, retain their normal texture, and revert back to their usual green colour after sufficient rain has fallen.

Near our lunch spot we found Thryptomene parviflora (photo above) had changed its normally green foliage to a glowing reddish-brown. The leaves were lustrous and alive, not dying as we tend to assume for brown leaves. Even more surprising, this plant was bearing a few fresh flowers (photo below).

Photo: John Elliott

We also saw the transition to diallagy in Hibbertia ferox (aka ‘Betsy’s fierce Hibbertia’) with some of its leaves still green while most of its foliage had changed to brown (photo below).

Photo: Julia Hazel

Pete sent in a very interesting article about diallagy in WA by Alex George, who coined the term in 2001. For copyright reasons, we can’t publish that article, but if you’d like to request a copy for personal use, you can Contact Us.