Black Mountain orchid walks 10th & 11th October

A big thanks to Sharyn Wragg for the photos on this page, which were taken during one of the walks.

Earlier this month Jean Egan and myself ran three guided orchid tours on Black Mountain, showcasing some of the diversity of native orchids found right on our doorstep in the centre of Canberra. Perhaps not many people are aware of our native orchid diversity, but by way of comparison, there are more species of orchid on Black Mountain alone (about 60 species) than there are in the whole of Britain (52 species).

This was the first year I had been involved in running these walks, but Jean and the late Tony Wood have been running these walks on Black Mountain almost every October since 2002. We initially only planned to run two walks, on Sunday morning and Sunday afternoon, but these rapidly booked out so we added an additional walk on Saturday afternoon.

After good winter rains, the bush was looking really good for the first time in three years, and the orchids were putting on a great display. We saw a total of 18 species of orchid flowering.

Starting out at the car park on the western side, we first talked about some basic aspects of orchid biology. Orchid seed is tiny and has little nutrients, so it requires the help of a mycorrhizal fungus which provide nutrients for the seed to germinate. Orchids are also famous for their intricate pollination systems, with many orchid species pollinated by only one or a few species of insect. Unfortunately, many orchids are rare and threatened, and because they are so delicate, trampling from orchid enthusiasts (or other traffic) can be quite damaging. We placed markers near orchid populations and asked that participants respected the markers and stay close to the path where possible, which everyone did.

Moving up from the carpark, we saw Calochilus platychilus, Diuris nigromontana, Caladenia atrovespa, Caladenia major, Hymenochilus bicolor, Pterostylis pedunculata in quick succession. We talked about how the Hymenochilus and Caladenia atrovespa produce chemicals which mimic the sex pheromones of female insects to attract the male insects as pollinators. Nearby, a big colony of Diuris nigromontana growing amongst pea flowers was a nice demonstration of how many Diuris species mimic pea flowers to deceive bees into pollinating without providing any nectar reward.

Not far away, we had the opportunity to compare Caladenia ustulata with the very similar Caladenia moschata, and the smaller Caladenia fuscata with the bigger, showier Caladenia carnea. We also saw our only Prasophyllum for the day, Prasophyllum brevilabre, a species which normally flowers after fire. Nearby, we saw some nice Paracaleana minor buds which were two or three weeks off flowering.

Most Pterostylis nutans were past their prime, but we managed to find one flower in good condition. A pleasant surprise was finding several Thelymitra carnea flowers just opening - these flowers only open on warm and sunny days.

Our newly published Field Guide to the Orchids of the Southern Tablelands, in the wild!

Proceeding up the hill, we added Diuris sulphurea and a little colony of the hard to spot Cyrtostylis reniformis which were just hanging on. One flower of Caladenia cucullata allowed us to smell the difference in scent between this species and Caladenia moschata, which can be quite obvious on warm days. We could only find one flower of Lyperanthus suaveolens this year, but nearby a lovely colony of Oligochaetochilus aciculiformis gave use the chance to talk about how greenhood orchids sexually deceive male fungus gnats which land on the labellum and are promptly catapulted into the top of the flower.

Checking orchid photos amongst a field of Diuris nigromontana — Checking orchid photos amongst a field of *Diuris nigromontana*

All in all, a lovely weekend blessed with fabulous weather and a great bunch of people. Until next year!