Davidson's Plum tree. Fruit of Davidson's Plum. Spacer
Left: D. jerseyana tree. This tree is tall, the fruit is collected from the ground; Right: Fruit of Davidson's Plum
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Davidson's Plum

Davidsonia spp.

Origin:

Native to coastal areas in Queensland and northern NSW. It is one of the four species that are cultivated commercially on a minor scale in these regions as an emerging Australian bush food industry. There are only three species in the genus – Davidsonia pruriens (PR), D. jerseyana (JE) and D. johnsonii (JO). PR and JE are given most attention in this entry as they are the two most commonly encountered; JO is relatively rare. JE and JO are classified as endangered species at national and state levels.

Climate:

The indigenous areas are warm temperate and sub-tropical rainforests - NE Qld up to elevations of 1000 for PR and NE, NSW lowlands for JE and JO. They all require consistent rainfall throughout the year. Mature trees can withstand light frosts but younger plants will suffer damage.

Plant Description:

JE and JO are basically smaller plants than PR. PR is tree-like whereas JE and JO are more bush-like with several branching slender stems. They all have dense crowns of compound leaves. New growth is pink-red covered in minute hairs. Mature deep green obovate-ovate serrate leaflets consisting of 3-7 pinnae are alternate imparipinnate with stipules; leaflets decrease in size towards the base. The rachis is winged. Tree parts of PR and JE are covered with long irritant bristly hairs but JO is glabrous.

Relatives:

They are members of the Cunoniaceae family which has no other commonly known edible fruits. JE and JO have previously been regarded as varieties of PR but the latest taxonomic and genetic evidence indicates they are additional and separate species.

Soil:

Not particular regarding soil type as long as organic matter is kept high. This not only retains and supplies nutrients but also helps maintain good moisture levels throughout the year.

Propagation:

PR and JE are grown from seed. Removing all pulp from the fibrous seed before sowing can be difficult. Seedless JO is propagated vegetatively by suckers or semi-mature cuttings.

Cultivars:

There are no named cultivars.

Flowering and Pollination:

Pendent inflorescences are cauliflorous or ramiflorous; in JO they occur more terminally within the leaf canopy. Individual apetalous pink-red hermaphrodite flowers have mainly 2 conspicuous curved styles longer than the 8-10 stamens. In PR, inflorescences are 30cm long panicles with 2-3mm anthers, in JE they are racemes or spikes 25cm long with 1-2mm-long anthers, and in JO styles are reduced or absent, shorter than the stamens and anthers have no pollen. Flowering occurs mainly from February to July for PR and October to January for JE. Bees are the pollinating agents, usually with self-pollination but occasionally also cross-pollination.

Cultivation:

PR is more tolerant of full sunlight than JE but both will still grow in partial shade. Mulching is beneficial and although prolonged waterlogging is not tolerated, low moisture levels should be avoided, particularly during flowering and fruit set.

Wind Tolerance:

In windy sites either windbreaks will be necessary or they should be planted amongst shelter trees.

Pruning:

Because inflorescences are cauliflorous, fruit yield is increased by pruning apical shoots to encourage growth of multiple stems.

The Fruit:

An obovoid drupe with a bluish-black skin and dark red/burgundy flesh, 30-45mm long X 30-50cm wide. Within the flesh there are 2 laterally-compressed pyrenes with soft fibres radiating from the margins; normally only one of the two seeds is fertile. Seeds within JO pyrenes are sterile. Fruit have better antioxidant levels (mainly anthocyanins and flavanols) than blueberries.

Fruit Production and Harvesting:

In ideal conditions, the juvenility period for JE can be as short as 1-2 years. Fruit mature normally within 3-4 months depending on local climate. Care should be taken with irritant hairs when harvesting.

Fruit Uses:

The fruit is an attractive plum-like shape and colour when mature, but even when fully ripe it is much too sour for almost everybody. Malic acid is the main acid contributing to this sourness. The flesh also doesn’t separate easily from the fibres radiating out from the pyrenes. It is consequently a fruit that is normally processed into various products such as jams, juices and sauces. With all of these, over-cooking will result in excessive breakdown of the vitamin C content.

Pests and Diseases:

They are resistant to root pathogens. Caterpillars, beetles and Qld fruit fly will damage fruit and parrots will eat both ripe and semi-ripe fruit. PR usually ripens in the autumn and winter when pest load is reduced.

Comments:

This is an attractive plant that can add an exotic, fern-like presence to a garden. Fruit yield can be plentiful given good conditions, but the most desirable form of processing will have to be established. Year-round constant moisture levels will need to be maintained and the ubiquitous hairs that are irritant to many people will need to be considered. It can be grown in a pot for many years.