Pittosporaceae

 

This relatively small Family, of nine or ten genera and somewhere over two hundred species of trees, shrubs and climbers, is found from Australasia, through Oceania to tropical Africa and India and into Eastern Asia. It is chiefly tropical and sub-tropical in its distribution but ranges into temperate climates at the margins.

 

The Family appears early in the evolutionary development of the Angiosperms and this situation is typified by the embryo of the seed being differentiated but small in size (immature) at dispersal. Thus the imbibed seed requires a period of exposure to warm temperature in order to achieve embryo maturity and hence an ability to proceed to germination.

 

Those species which fringe into temperate climates include members of the Australian genus Billardiera (which now includes Sollya) and members of the largest and most widespread genus, in the Family, Pittosporum. The monotypic genus Hymenosporum flavum is grown in warm temperate climates often as street tree.

 

Billardiera

 

The genus Billardiera consists of about twenty four species of woody climbing plants which are all native to Australia; most are not suitable for cultivation in the UK but the relatively hardy, sparse growing B. longiflora is often seen – it is grown for the coloured fruits which vary from white to pink to red to purple to blue (and these variants generally come true from seed). Also seen are the two species of Sollya (B. heterophylla and B. fusiformis) - the Australian Bluebell Creeper.

 

The fruits are sausage to block shaped, locular, fleshy capsules about 15 to 20mm long and 10 to 15mm broad; these have a brightly coloured skin. The seeds are readily extracted when the fruits are ripe. The many seeds are contained in a sticky mass and the fruits are simply split open by hand and the ‘mess’ separated – this is then washed to clean the seeds which are then surface dried.

 

To achieve germination the imbibed seeds are warm stratified at 25˚C for twenty one days in order to mature the embryo. The treated seeds can then be sown and maintained at 18 to 20˚C, in the propagation environment, when emergence will occur in seven to ten days.  

 

Pittosporum

 

The genus Pittosporum contains about two hundred species of trees and shrubs, which has an extensive distribution from Australasia through Oceania to Eastern Asia - with outliers in Africa. At the northern and southern geographic extremes they fringe into temperate areas. They are evergreen or deciduous.

 

The following species are all hardy to some degree in the UK, but most will require a mild niche in order to flourish - P. bicolor (South East Asia); P. daphniphylloides (China and Taiwan); P. tobira (Japan); P.crassifolium, P. dallii, P. eugenioides, P. obcordatum, P. patulum, P. tenuifolium inc P. colensoi), P. ralphii and P. turneri (all New Zealand) and P. phillyraeoides and P. undulatum (both from Eastern Australia).

 

The highly scented, often colourful flowers are produced during the summer. The fruit is a capsule, initially somewhat fleshy and often brightly coloured but which dries to a woody condition and then dehisces violently. The seeds are covered in a black sticky pulp which keeps the seeds adhering to the flat, opened capsule case for several days. The seeds can then be picked off and washed clean.

 

The imbibed seeds are then warm stratified for twenty one days at 25˚C to complete the maturation of the embryo. Germination is then possible at 20˚C but in virtually all of these ‘temperate’ species the process will be attenuated and erratic. Chilling the seed at 3˚C for twenty eight days, after embryo maturation, will unify, synchronise and speed germination.

 

Hymenosporum

 

The ‘Native Frangipani’ (Hymenosporum flavum) of Queensland and New South Wales is a small evergreen tree with dark glossy green leaves. It is widely cultivated in Australia and California. It produces, in Spring, cream flowers which age to yellow and are 5cm across, they are highly scented - the scent is very similar to Frangipani.

 

The fruits, which ripen after midsummer, mature as long pear-shaped capsules which ripen to a purple-brown colour and are somewhat woody. At maturity the capsule splits into two and exposes the seeds, these are small, brown and have a membranous wing.

 

There are no constraints to germination except insofar as the embryo has to mature before the germination process will begin. If the imbibed seeds are sown at 25˚C they will mature the embryo and germinate satisfactorily at that temperature and emergence will occur in thirty five to forty two days.