Common name: Red stringybark

Red stringybark is an Australian eucalypt valued for its leaves, which contain a compound used in the preventative treatment of conditions associated with vascular disease.

Its natural range is limited to eastern Australia, where it occurs in warm-temperate and subtropical areas extending from Central Victoria, in the south-east of the continent, to the Southern, Central and Northern Tablelands of New South Wales.

It may grow to become a large tree on favourable sites, to heights of up to 35 m (115 ft) with a trunk diameter of 1 m, though it is more commonly 15 to 20 m (50 to 65 ft) tall.

The trunk is usually straight, clear of branches for about half to two-thirds the tree height and supports a rounded, moderately leafy crown of ascending branches. The bark is grey to red-brown, stringy and with deep longitudinal fissures.

As with many eucalypts, the leaves change shape as the tree matures, the leaves on juveniles ovate and dark glossy green, those on full-grown trees narrowly lanceolate, up to 15 cm (5 in) long and dark dull green. They persist on the tree throughout the year.

The flowers are typical of eucalypts, with long white filaments arising from a small cup-shaped base. They come into bloom from summer to early autumn, held in clusters of a few at the sides and ends of the branches.

The fertilised flowers develop into small, green, bowl-shaped seed capsules up to 1.2 cm (0.5 in) wide, becoming brown and woody when mature with small dark brown to black pyramidal-shaped seed inside.

Use

The wood is medium to heavy, in the 630 to 950 kgs per cubic meter (39 to 59 lbs per cubic foot) range, and has moderate to good natural resistance to rot, decay and wood-boring insects. This puts it in the durable hardwood class, suitable for both indoor and outdoor applications. The sapwood is pale brown, and the heartwood light pink-brown.

Suitably sized logs are sawn into beams and planks used in construction, including house construction, fencing, indoor flooring, as well for making furniture and cabinets. Small-diameter logs are widely used for posts and poles. The off-cuts and branch-wood should make excellent firewood and charcoal.

Red stringybark is a honey tree, but nectar flows are abundant only every two to five years and unreliable from trees in low rainfall areas. At peak nectar flows, honey yields are up to 60 kgs (132 lbs) per colony per season. The honey is deep amber with an earthy, toffee-like flavour and rarely crystallises. Its high lustre makes it keenly sought after for blending with other, less lustrous honeys.

Health use

The leaves contain high concentrations of the compound 'Rutin', also known as 'Vitamin P', a natural bioflavonoid antioxidant with preventative action against capillary fragility and haemorrhage, mainly brought on by degenerative vascular diseases, such as arteriosclerosis and high blood pressure.

Red Stringybark leaves are the primary source of Rutin, and commercial extraction has been undertaken for many years in Australia, the leading producing country and exporter. 

From 10,000 to 12,500 kilograms of fresh leaves are harvested per hectare per year in commercial plantations, with an average Rutin content of 5%, yielding 500 and 625 kilograms of saleable Rutin, the equivalent of 446 to 558 pounds per acre.

The harvested leaves are first air-dried at temperatures between 80 and 100°C (176 and 212°F), then ground and boiled in water to extract the Rutin. The resulting filtrate is then cooled, and the Rutin is crystallised out and dried. From a technical perspective, the extraction process is inexpensive and straightforward. It yields a relatively pure Rutin, which is usually in the form of a yellow powder.

Climate

Grows naturally in warm-temperate and sub-humid to moderately humid subtropical climates, generally areas with annual lows of 5 to 15°C, annual highs of 18 to 27°C, annual rainfall of 500 to 1600 mm and a dry season of 7 months or less.

Growing

New plants are started from seed sown in containers with a free-draining potting mix and cared for in a nursery until they are ready to be planted out when around 30 to 50 cm (1 to 1.5 ft) tall. The seed lose their viability quickly and need to be sown soon after extraction, or they may be stored for a short period under cool, dry, airtight conditions. Germinates rates are low, usually under 10%.

Performs best on free-draining clay, clay-loam and loam soils of a moderately acid to neutral nature, generally with a pH of 5.5 to 7.5, and on sites with full sun exposure.

During the first three years, the plants are trained to a moderate height to facilitate mechanical harvesting. They are harvested for their leaves three times over twelve months. Harvesting continues for around ten years, after which the Rutin content in the leaves becomes too low to make harvesting and extraction economically feasible.

Problem features

There does not appear to be any record of it anywhere as a weed or invasive species.

Books

• Boland, D. & Brooker, I. & McDonald, M. W. 2006, Forest trees of Australia, 5th ed., CSIRO Publishing (Ensis), Melbourne

• Brady, G. S. & Clauser, H. R & Vaccari, J. A. 2002, Materials handbook : an encyclopedia for managers, technical professionals, purchasing and production managers, technicians and supervisors, 15th ed., McGraw-Hill, New York

• F. R. Beuhne 1922, Honey flora of Victoria, Melbourne Albert J. Mullett, Govt. printer

• Farooqi, A. A. & Sreeramu, B. S. 2004, Cultivation of medicinal and aromatic crops, Hyderabad University Press, Hyderabad

• Hall, N. 1972, The use of trees and shrubs in the dry country of Australia, Australian Government Publishing Service, Canberra, Australian Capital Territory

• Khan, I. A. & Abourashed, E. A. 2010, Leung's encyclopedia of common natural ingredients : used in food, drugs and cosmetics, 3rd edition, Wiley Publishing, Hoboken, New Jersey

• Leech, M. 2013, Bee Friendly: A planting guide for European honeybees and Australian native pollinators, Rural Industries Research and Development Corporation (RIRDC), Canberra, Australian Capital Territory

• Scheffer, T. C & Morrell, J. J. 1998, Natural durability of wood : a worldwide checklist of species, Forest Research Laboratory, Oregon State University, Corvallis, Oregon

• Winter, R. 2009, A consumer's dictionary of cosmetic ingredients : complete information about the harmful and desirable ingredients found in cosmetics and cosmeceuticals, 7th ed, Three Rivers Press, New York