Acacia phlebophylla, a type of acacia also known by the names Buffalo Sallow Wattle and Mountain Buffalo Wattle, is a straggling shrub to small, twisted tree reaching up to 5 m in height. It is a close relative of Acacia alpina.It has large, elliptic, flat, commonly asymmetrical phyllodes 4–14 cm long, 1.5–6 cm wide, with coarse veins, a leathery feel, prominent nerves and reticulated veins. Deep yellow rod-like flowers appear in spring (June–December in Australia), widely scattered on spikes 4–7 cm long, followed by 7–10 cm long legumes in November–March, narrow, straight or slightly curved, releasing 5-10 elliptical seeds, 5-7.5 mm long. Solitary or twinned spikes, to 6 cm long. Only known from the high altitude granite slopes of Mount Buffalo National Park, Victoria, Australia, where it occurs above 350 meters in woodlands and heathland often amongst granite boulders (From Wikipedia)
For many years this species has been regarded as being extremely difficult to establish outside its native range and in cultivation. Several cultivation attempts using different media and even tissue culture have failed dismally.
I assumed that the degree of difficulty in establishing this species in cultivation may have been due one of two factors; climatic conditions (although A. phlebophylla would be assumed to be quite resilient as it clings to a mountain side and can be subject to very high and very low, even snowy conditions at times of the year) or lack of a rhizobial bacteria or mycorrhizal fungi symbiont that is important or critical to their well being.
Mycorrhiza are fungi that live in the soil, or within plant roots, that form a mutualistic relationship with the plant, allowing the plant greater access to nutrients and water and in return the fungi receives carbohydrates. More info here : http://en.wikipedia.org/wiki/Mycorrhiza
Rhizobial bacteria live in the soil and can take up residence in special root nodules that are unique to those in the legume family and include Acacia, Soybean, Bean, Pea amongst thousands of important crops. More info here: http://en.wikipedia.org/wiki/Rhizobia
I tried a few batches of seed I had received as a gift with different treatments. With limited success simply subjecting the seeds to hot water treatment gave a few seedlings with varying survival, most not living very long. Hot water treatment and mycorrhizal fungal treatment provided similar results. Hot water treatment and a commercial Acacia rhizobia inoculant provided good germination over a period of 6 months (this is normal i find with A. phlebophylla, seeds can lay in the soil untouched by insects or bacteria, fully imbibed with water, simply waiting for an external trigger, which I often found to be a good thunderstorm event). From germination onwards the seedlings were strong and healthy and have continued to grow well under 50% shade conditions in SE QLD Australia, summer 2013-2014, a particularly hot and low rainfall summer so far.
The inoculant was supplied by Becker-Underwood, and when I recently tried to purchase more was told that they had ceased to make this particular inoculant. More searching and it looks as though no one in Australia is now making an inoculant for Acacia, which does sound as ridiculous as it is. Luckily A. phlebophylla appears not worried about having a particular rhizobia and a promiscuous species or mixed strain inoculant can do the job.
For the trial the seeds were prepared as follows: subject to hot water treatment (boil kettle and pour just boiled water over seeds and let stand overnight), slurry of inoculant was applied to seeds and once seeds were planted, they were watered in with remaining inoculant slurry, which is often called inoculation by soil enrichment. Once seedlings emerged, they were mulched with a 7mm basalt gravel and this appears to help them by stopping moss growth and perhaps providing micro nutrients. It’s also aesthetic!
Whilst it is as simple as it sounds, I hope this technique enables this important species to be grown more widely in different parts of Australia. It is probably the most beautiful Acacia I have seen, especially in habitat. Check out the photo of the thick phyllode below.
This is the outcome we want to see, flowering specimens in cultivation Australia wide.
Update 3/3/2014: The seedlings are progressing well and a few have been sent out to growers around the country. No losses in the nursery so far. I have noticed they benefit at this stage by going into a more open position, 100% sun for at least a few hours per day. The root system is well established in the plants pictured in pots above, many nodules were observed on the roots and the typical sharp/vinegar smell associated with rhizobia bacteria was present. A notable feature was the absence of a tap root on the ones I have sent. This could be advantageous to this species being kept in pot culture as a tap root is not a benefit and the longevity could be maintained without the need to be planted out. Living on the side of a granite mountain, A. phlebophylla would benefit from a branching root system with no central tap root, a strong rhizobial partnership and most likely a mycorrhizal association for added nutrient and water uptake.