WA 2019: Part 6. Granite Outcrops and Salt Lakes

WA 2019: Part 6. Granite Outcrops and Salt Lakes

At the end of winter in 2019 I embarked on a 17 day expedition to document the carnivorous plants of Western Australia. I drove thousands of kilometers and photographed over 50 species in their habitat.

Previous: Part 5. South Coast Heath and Mallee

The Wheatbelt region is named for its extensive plains, which have overwhelmingly been cleared for agriculture. Pockets of indigenous biodiversity occur within the sparse nature reserves, which are mainly centred around the geographical features in this harsh landscape. Here, ancient granite inselbergs the size of hills rise dramatically out of the surrounding fields and most permanent watercourses are saline from the accumulation of minerals over millennia. It is around these outcrops and salt lakes that I focused my attention for the next few days, allured by rumours of the rare sundews that congregate around them.

As I approached the first granite outcrop, nothing could have prepared me for the sheer scale of everything I was about to experience. These giant red monoliths were simply huge, and I was surprised by how lush the areas around them were. As I approached the rock, I noticed that the scrub was covered in a strange orange growth. I quickly realised in awe that this was actually masses of Drosera subhirtella and macrantha that grew so thickly they blanketed the ground and surrounding bushes. Walking onto the rock surface, I immediately noticed that the thin layers of moss that covered the wetter areas were studded with thousands of D. lowriei. Star shaped D. bulbosa, coloured in shades of yellow and red covered the peaty outwashes like confetti after a festival. I spent almost hour wandering the rock surface, which must have occupied around a hectare in space, finding orchids and sundews wherever I looked.

I had a few more sites marked out for exploration that day, and with enthusiasm I drove off to another outcrop. This one was covered in Drosera glanduligera, which grew so densely that the ground was endowed with a metallic glow. At the following rock, thousands of Drosera graniticola occupied its base. This species is notable for producing a massive floral inflorescence with more than 20 concurrent white blooms. The entire field was beautifully covered in white flowers, with a display that surely rivals the non-carnivorous wildflowers that the region is known for. I found sundews growing en mass at each new outcrop and every site seemed to have a species that dominated.

Drosera graniticola

But the goal I had set for the day was to find two rare species of sundew with enigmatic niches that I wanted to better understand. Drosera salina and zigzagia grow only around salt lakes in the Wheatbelt. It confused me as to how this could be – as high mineral contents are usually detrimental to carnivorous plants.

Drosera zigzagia

By now it was late afternoon and rain clouds were starting to develop, so I hurried off to visit a salt lake site that I had been tipped off about. I was surprised to find that this ‘lake’ was only the size of a large pond and was a lot smaller than some of the systems I had poked around earlier in the day. As I walked towards the water, I suddenly found that I was surrounded by a field of Drosera zigzagia! As its name suggests, the tiny species has zigzagging erect stems that reversed direction at every leaf node.

Drosera salina with a Setocoris sp. bug

My attention then turned to Drosera salina and I walked to the other side of the lake, but I was confused at its absence. I returned to the water line to inspect it more closely and found that I had literally walked right past the plants, not noticing them as they were so small! Compared to the golden leaves of D. zigzagia, D. salina is coloured a dark red and has stems around half as tall. The species has a substantial basal rosette, but this is always buried under a layer of crystalline silica sand. Interestingly, while the two species grew within meters of each other, they never intermixed. D. salina grows on sloping surfaces close to the edge of the lake, whereas D. zigzagia prefers flat ground elevated from the shores.

Suddenly a downpour developed, and I was forced to cut my exploration short and run back to the car. I decided that it was about time I made my way to my accommodation in Hyden, which was still a good hour’s drive away. Of course, the spirit of exploration overcame me, and I stopped at one more site that I had marked on my map.

I’m glad I did stop as it was only after seeing this location in the rain that I truly appreciated the ecological role of the outcrops in the Wheatbelt. Small cascades of water had formed in the weathered channels on the rock surface and gathered in deep pools of water around its base. I came to the realisation that these giant impermeable surfaces are very effective at collecting and concentrating rainwater, forming seasonal accumulations of moisture that support the hundreds of endemic species of the area. Drosera rupicola, a large sprawling species of fan-leaved sundew, grew in full bloom at the edge of the water pools whilst D. lowriei and bulbosa were temporarily submerged under a stream of fresh water. Soaked and exhausted, I finally resigned back to the car after a very overwhelming day of exploration.

Hyden is known for its tourist attractions, which mainly consist of various popularised geographical features. The following morning, I decided I might as well do some standard sightseeing, so I woke up early and made my way to Buckley’s Breakaway, a naturally eroded gully with dramatic rock features. I suppose the landscape was interesting but I was disengaged by the lack of Drosera so I quickly took some photos and made my way over to Wave Rock. This iconic eroded feature lies at the base of the massive Hyden Rock and is shaped like a wave. I arrived when it was still too early for the regular tourists and had a lot of fun running up its side.

Naturally, I turned my attention to finding sundews and I soon found myself scaling the absolutely gigantic inselberg. The surface of the outcrop was so large that it hosted a range of niches, complete with streamlets, bushes, and moss aprons all entirely elevated from the plains. Drosera bulbosa grew freely where loam had accumulated and D. yilgarnensis, a western member of the D. peltata species complex, occupied the mossy patches on the edge of bushes. I continued to a few more locations within the tourist park and found species like D. macrantha and D. rupicola. Whilst these were nice to see, I couldn’t help but notice how the area was disturbed by the thousands of tourists that visited them.

The salt lake sundews were still very much on my mind and the site I had visited yesterday left me with questions regarding their ecology. So, for the remainder of the day, I resolved to find more populations of the plants which is no easy task given that their exact locations are not publicly available. Thinking back to what I had learned the previous day, I found a promising site on the satellite and promptly made my way there.

Drosera andersoniana

I drove as far as the car could take me and followed a farming trail to an outcrop at the edge of system of shallow salt lakes. Around the outcrop, I saw a field full of Drosera andersoniana growing amongst the grasses. After a while of bush bashing in forest, I finally broke out to the open sandy shores of the lake – but no sundews could be seen. Remembering that D. zigzagia preferred elevated flat plains, I walked along the perimeter of the woodland until I came to a wide-open area and sure enough the species was there! The plants at this site were in full bloom and I was enamoured by their pastel yellow flowers. It seemed that the plants weren’t particularly rare provided that their niche of flat quartz plains was present. However, D. salina could not be seen anywhere nearby.

Drosera zigzagia at a new location

A bit perplexed by its absence, I re-examined the situation and recalled that Drosera salina was spatially segregated from D. zigzagia and seemed to grow only on sloped surfaces. Perhaps the seepage of water out of surrounding elevated bushland was needed by the species? For that to occur, it would require a particularly deep salt lake, as an elevation gradient between the saline lakes and fresh groundwater layer had to be present. Regathering, I found another site off Google maps around 50 km away and promptly made my way to it.

At this site, a granite outcrop adjoined a large salt lake, so I thought that the area where freshwater from the rocks drained into the quartz field of the lake might provide the ideal habitat. This location was well off-road and required a bit of navigation to reach. I managed to find an old trail and followed it until I got near enough to the outcrop, after which I pushed through the scrub to reach it.

As I stepped onto the rock surface, I was presented with the most beautiful sight of the day. The remote outcrop was surrounded by undamaged fields of Drosera graniticola growing en mass. Against the vivid blue sky and the rusty coloured rock, the plants caught the rays of the low afternoon sun and illuminated the fields with a glowing copper aura. I also found substantial amounts of D. yilgarnensis and stricticaulis growing in pockets of moss on the rock. Traversing the outcrop towards the lake, I took great pleasure in the natural surrounds, watching the sundews sway gently in the breeze with the warm sun against my back.

Drosera salina
Drosera salina

Finally, I reached the salt lake and my eyes were immediately drawn to the patches of red on the sandy banks of the streamlet that drained from the outcrop! Thousands of D. salina grew at this location, providing a highlight to cap off an already perfect day. Equally stunning was the fields of D. zigzagia that grew in the flat plains higher up.

Drosera zigzagia
Drosera zigzagia

After observing the plants at this extensive site, I finally began to understand their respective niches. Both species require a coarse quartz substrate, which is deposited by the permanent saline watercourses in the Wheatbelt. Whereas D. zigzagia requires a deep sand base, D. salina additionally requires a sloping surface and appears to occupy the thin zone where ground water seeps out from the surrounding bushland, perhaps benefiting from the deposition of some mineral component. This elevation gradient is rare, only forming around the deepest salt lakes, and explains why D. salina is much more uncommon than D. zigzagia. I spent the rest of the daylight at the site, photographing the plants in the rich glow of the setting sun.

Having located all I had set out to find in the Wheatbelt, I drove back to Perth the following day, using the occasional outcrop as rest stops. At the first site, I found Drosera monantha growing amongst the grasses. The large rosetted species was a surprising find and I wasn’t even aware that it existed at the time! At the next location I unexpectedly saw a small patch of D. ramellosa growing in a moist mossy pocket in granite. This species in the Stolonifera complex was can be distinguished from its fan-leaved relatives by its erect stems and flowers that emerge directly from its basal rosette.

It wasn’t long before I reached the base of the Darling Scarp, a band of hills that runs parallel to the coast and separates the Wheatbelt from the ocean. To reach Perth, I would have to drive through the densely forested area, which is fed by high rainfall from orographic lift of the humid coastal winds. I still had a few hours of daylight left so I took the opportunity to take a hike and find some plants.

In the hills, the frequent rain often exposes the granite base rock to the surface, especially around the many creeks that flow in the area. A goal of mine was to find Drosera gigantea, which grows abundantly in waterlogged soils in the area. I was successful in locating the early growth stage of the species, which has an uncanny resemblance to asparagus shoots, but it was still too early to see any mature plants. I also saw plenty of the rosetted D. rosulata and erect D. menziesii, which were both vivid red in colour, growing in the loam around the watercourses.

I finally arrived back in Perth as the sun set, completing my very long circuit of south-west Western Australia. I had driven some 700 km in the past three days alone, but my trip was far from over …

Next: Part 7. Northern Sandplains and Laterite Slopes

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