Sizing up the Syzygiums – some shockingly similar satinashes

Some time back, I wrote a post on Sizing up the Syzygiums as a general guide to “leaf whispering” this large group of very similar looking species commonly called lillipies or satinashes.

After being able to look for certain spot characteristics such as flanging on the internodes (the stem sections between successive new leaf growth) and details of venations, it is possible to finally start seeing differences between different species of Syzygiums.

Yet some of the more common Syzygiums still occassionally stump me.

And here I am referring to Syzygium australe, Syzygium olesum and Syzygium smithii.

This is why:

They are all typically small trees to tall shrubs, have flanged stems, and elliptic to slightly obovate leaves. The leaves of theses species also tend to have depressed midribs. They are also sometimes found growing under similar conditions, such as along rainforest edges or in the eucalypt forest with rainforest understoreys.

Fortunately when flowering or fruiting they are quite distinct from one another, but the challenge is to be able to distinguish them when they are not in flower or fruit.

So lets begin.

Differences in stem flanging

Syzygium australe, the Creek Satinash, is probably one of the more common satinashes in the region. It is also widely grown in gardens. Among the three species, it has the most developed stem flanges, which in young shoots may have a slight red tinge.

Leaf sheen

S. australe and S. smithii have rather shiny bright green leaves, but in the field I have often observed that this sheen is brightest in S. australe. S. oleasum tends to have the darkest tone of green among the three

Visibility of oil dots

Also compared to S. smithii, S. australe has less visible oil dots when you hold the leaves up against the light.

Inflorescence differences

The differences when the three are in flower are quite marked.

S. australe often has 3 flowers, but sometimes more. The flowers are quite large and showy (the stamens “explode” outwards giving the flower a bit of a pom-pom look). Syzygium oleosum has similar showy flowers, but the inforesences look somewhat more pendulous.

S. smithii is probably the most different from the two, with very small flowers and a much more complex branched inflorescence.

Smell of crushed leaves

Syzygium oleosum is instantly recognizable from the other two from the smell of the crushed leaves, which has a more turpentinish or peppery smell. In contrast, the crushed leaves of S. australe and S. smithii have a sweeter, milder scent.

Note

It is probably worth noting that Syzygium australe can be quite variable as there appears to be quite a number of varieties of the species in cultivation.

Rhysotoechia robertsonii (Sapindaceae)

Orange and green makes for a stark an arresting contrast in a rainforest, and that is what would likely compel an inquisitive nature lover to walk up and inspect closer.

On closer inspection, one finds the gorgeous shiny black “eyes” that are the exposed seeds “looking” back. It is all part of the seductive maneuvers of the Sapindaceae.

Indeed, most of the rainforest Sapindaceae employs such a maneuver ̶ brightly coloured fruits which split open to reveal a shiny seed (sometimes covered by fleshy tissue called an aril).

In the case of Robert’s Tuckeroo (Rhysotoechia robertsonii), the fruits are bright orange and split open to display three black shinty seeds. Where the seed connects to the inner fruit wall, it is also possible to notice a yellow fleshy aril.

The leaves are compound, with around 6 or more (up to 10) alternately arranged leaflets on the rachis that have a very short or absent stalk. The leaves resemble Guioa acutifolia but are not glaucous on the underside.

iNaturalist entry: https://www.inaturalist.org/observations/67164775

Dipodium ensifolium (Orchidaceae)

Few plants enliven a savanna as much as a glorious blossom of orchids.

This is definitely the case with the Leafy Hyacinth-orchid (Dipodium ensifolium).

The blossoms are showy, and bear a structural resemblance to a hyacinth, with up to 20 pink to mauve flowers with purplish blotches and spots

This attractive terrestrial species is endemic to northeast Queensland and inhabits forest and woodlands between Cooktown and Ingham.

Growing among savanna grasses, plants of the Leafy Hyacinth-orchid and can become quite lanky (up to 1m long), but when their aboveground parts are burnt they appear to be able to resprout readily from their underground tubers.

The species is probably very well suited for cultivation and deserve to be grown as an ornamental plant in open areas.

See iNaturalist entry: https://www.inaturalist.org/observations/66780125

Flindersia pimenteliana (Rutaceae)

Flindersia pimenteliana is commonly known as Maple Silkwood and is a relatively common tree in the lowland and upland rainforests of the region.

The leaves compound and opposite. The compound leaves are pinnate, typically with 5 leaflets – 2 pairs of opposite leaflets and one terminal leaflet. Leaflets shiny green above and conspicuously lighter below.

The fruits are distinctive of the genus. These consist of rather large rough surfaced capsules which dry brown and split open into five segments to release winged seeds.

The species is also found in PNG.

See iNaturalist entry: https://www.inaturalist.org/observations/65075553

Cymbidium madidum (Orchidaceae)

Epiphytic orchids are a common feature in tree dominated habitats in the Wet Tropics, and one of the more common epiphytic orchids in the region is the Giant Boat-Lip Orchid (Cymbidium madidum).

The orchid is probably one of the most environmentally resilient epiphytic orchids in the region. It grows in a wide variety of forest environments ranging from rainforest to open savanna woodlands, and from lowlands to uplands.

Where I am living now, the orchid is commonly found on wattle (Acacia) trees of secondary forests, but I have seen them growing on paperbark trees in swampy habitats and also on rocks as well. Plant grow to form clumps that can be huge, reportedly up to over 2m across.

The attractive yellow flowers hang downwards and have a sweet scent, and the species makes for a wonderful ornamental. Sometimes clumps get too heavy and drop off forest trees, and it is easy enough to salvage , graft, and re-establish them onto other trees in a garden.

My iNaturalist entry:
https://www.inaturalist.org/observations/64636733

Decalobanthus peltatus (Convolvulaceae)

Lianas are a conspicuous component of tropical rainforest, but in the case of this vine, one may argue it is far too conspicuous.

Decalobanthus peltatus is a very large and vigorous species that comes up after disturbance, particularly after cyclones have damaged the canopies of rainforests. It is not unusual therefore to find it smoldering the canopies of even some of the tallest of our rainforest trees. In that way, it is one of those contentious native species that can become weedy in their native environment.

Photographed at the Daintree

The liana has an aptly assigned species epithet, peltatus, which refers to the way the leaf stalk is inserted within the leaf margin (a peltate leaf). The stems can get huge, up to 9cm wide, which is quite large for a vine, and when cut exudes a pale yellowish sap. The water transporting vessels in these stems are also so huge that they can be seen with the naked eye.

When they flower, Decalobanthus peltatus is undoubtedly an attractive species and the large white blossoms betray their affinities with the morning glories (the Convolvulaceae). One could perhaps think of this species as a giant morning glory.

The plant has some medicinal uses in some Asian countries where it occurs, and the tubers are known to be edible.

For a long time this species was known as Merremia peltata, but a publication in 2017 by Simões and Staples changed all this. Bringing together evidence from floral morphology, pollen morphology and molecular data, they found that the genus Merremia was not monophyletic, that is, the species in Merremia didn’t all fit very well within that genus. To cut a long story short, what was once conveniently known as Merremia peltata is not Decalobanthus peltatus.

See my iNaturalist entry:
https://www.inaturalist.org/observations/62689242

Geodorum densiflorum (Orchidaceae)

Orchids are always a delight.

As a botanist with a bit of a history with orchids (I once interned at an Orchid cultivating laboratory), I have a soft spot for orchids.

While cultivated orchid varieties are always glamorous, I have always been drawn to native orchids. It doesn’t really matter which country I am in, just the mention of native orchids get me excited.

This excitement doesn’t get dulled by how common an orchid is – I haven’t yet encountered an orchid that doesn’t delight me.

In the north Queensland region, it seems like one of the most common ground orchids is the Pink Nodding Orchid (Geodorum densiflorum) or Sherperd’s Crook Orchid, referring to the distinctively bent inflorescence

“Geodorum” is derived from the Ancient Greek words ge meaning “earth” and doron meaning “leaf”, and refers to the terrestrial habit of orchids in this genus. The species epithet “densiflorum” refers to the dense flower arrangement.

The species is listed as “endangered” under the New South Wales Government Threatened Species Conservation Act 1995, and also as endangered in iNaturalist, but in Cairns it comes up spontaneously in well-mulched garden beds in the city. Perhap it is all well to call it endangered if it helps the public to threat it with more care. The species is also found widely in tropical Asia and other Pacific Islands.

When not in flower, the species can look superficially like another terrestrial orchid Dienia ophyrys.

See my iNaturalist entries:
https://www.inaturalist.org/observations/48220841

 

Blighia sapida (Sapindaceae)

Years ago, whilst walking along the streets of a northern suburb of Cairns, a red fruit caught my attention.

It was a large capsule the size of a huge egg, which split open very neatly along three suture lines and opening up to revealed beautiful shiny black seeds donning an cream white aril.

The tree in general was rather attractive, having robust compound leaves which have a little ‘pin’ at the end of each compound leaf rachis.

The fruit and leaf characteristics immediately allowed me to identify this as a species of the Rambutan family (Sapindaceae).

I collected it and tried looking it up in using the seminal work by Wendy and William Cooper’s Fruits of the Australian Tropical Rainforest and also the online rainforest plant key by Bernie Hyland and collegues. I found nothing.

Sometime when a specific identification key fails, google works. It occurred to me to type in the search terms “edible Sapindaceae” and a picture that looked like my mystery fruit surfaced.

And thus was the identity of my mystery fruit cracked.

It was the Ackee, Blighia sapida, a native of West Africa.

It is also known under another interesting name, the vegetable brain, due to the appearance of the aril, as well as some other variants of its name such as achee, akee apple, and akee.

It has a broad suite of uses. The white fleshy arils of Ackee is toxic when upripe or uncooked and has to be properly prepared before eating. The dried seeds, fruit bark and leaves are used medicinally and the fruit is used to produce soap in some parts of Africa. It is also used as a fish poison. I have also written more of this in Respecting the Vegetable Brain. 

The species is native to West Africa but has been introduced to various countries and has become a prominent component of Jamaican culture. It’s uses are much less well known in Australia though.

The flowers of the ackee tree are also quite large, as far as Sapindaceae flowers go.

See iNaturalist observations:
https://www.inaturalist.org/observations/47725711
https://www.inaturalist.org/observations/47719442

Balanops australiana (Balanopaceae)

I was having a jog through the woods and noticed a bunch of twigs of an unfamiliar plant that had been brought down either by wind or breakage by birds.

I will admit it. This species took me quite a long time to get an identification on, even though there were mature orange fruits on the twig. These cute fruits look like little orange oak acorns. Indeed, the genus name Balanops refers to the this resemblance (balanos = acorn and opsis = resemblance to), although the plant is not relation closely related to oak trees.

Other than those fruits, the leaves were somewhat obovate, alternately arranged, and had no stipules, and therefore very generic. My first impression was that it was a Diospyros, a member of the Ebony family (Ebenaceae) because of the way the fruit sits on a set of bracts. However I could not match the sample up with any of the pictures or illustrations of Diospyros in the region.

Utimately nothing beats just flipping through Wendy and William Cooper’s Fruits of the Australian Tropical Rainforest book to find an answer.

Supposedly, this tree has bark with very obvious whitish lenticels (breathing pores), hence the common name pimplebark or pimply ash.

Balanops australiana is a pleasure to tick off on one’s botanical bucket list because the genus is the only one in the family Balanopaceae, and also because it is shows an interesting connection of Australian rainforests with those of New Caledonia and Vanuata, which are where one may find other species of Balanops.

Asplenium simplicifrons (Aspleniaceae)

Aptly named the Narrow-leaf Bird’s Nest Fern, this epiphyte or lithophyte is restricted to rainforests and does not seem to be as common as the larger A. nidus or A. australasicum. However, it is always a pleasure to spot this fern and it makes for a beautiful ornamental plant to grown in shaded gardens.

Like the two other related bird nest fern Aspleniums, the fronds of this fern are simple and the sori (the spore-bearing structures) are linear and slit-like and stretches from the midrib to near the leaf margin.

See iNaturalist observation:
https://www.inaturalist.org/observations/47249660