Alyxia ruscifolia subsp. ruscifolia

Posted on Updated on

Alyxia ruscifoliaFamily: Apocynaceae
Genus: Alyxia
Common names: Chain fruit, Prickly Alyxia
ALA reference

The insect we found on the plants has been identified as Thrips setipennis. This species of thrips is known to be the pollinator of Wilkeia huegliana and Myrsine variabilis so I think there is a good chance it is also pollinating the Alyxia ruscifolia. Incidentally our one and only plant of Wilkeia huegliana is now covered in buds and will flower for the first time in a month or so. It will be interesting to see if it sets fruit.

(July 2012)

This species has flowered spectacularly this year and anyone walking through the reserve could not fail to have noticed the delightful perfume that these plants are releasing. However it suddenly occurred to me that I had never seen a bee, fly, butterfly, moth or any other insect visiting these flowers. It is also interesting to observe that even though these plants have thousands, even possibly tens of thousands, of flowers, they set very few fruit. It is rare to find a plant in the reserve with more than about 30 fruit and many have only 6 to 10. So the obvious questions are how are the flowers pollinated and why do so few flowers set fruit?

To try to answer the first question, I took home a few flowers for dissection. The first thing to note is that the flowers are about 7mm long and 5mm across the petals. The small round hole in the head of the flower is about 0.25 to 0.30 mm in diameter. When I opened the tube of the flower I discovered that the inner surface was covered in small downward pointing hairs. It seems therefore that the flower must be pollinated by a small flying insect that has a body diameter of less than 0.25mm. On entering the flower though the small hole in the top the insect would be forced to the bottom by the downward pointing hairs where its only method of escape is to climb the style, then over the stigma and then brushing past the pollen to finally escape through the hole in the top of the flower.

While I was considering these possibilities a small thrips dropped from the flowers I had collected. It is about 1.7mm long with a body diameter of about 0.2 to 0.25 mm. I believe there is a good chance that this is the pollinator as thrips are known to pollinate some species of flowers and its body size is perfect for the task. After discussions with Dr. Paul Forster at the Queensland Herbarium, Hazel and I collected some more thrips from the flowers in the Reserve for Paul to send to Canberra for identification and further investigation.

However this doesn’t help answer the second question as to why so few flowers are pollinated. If this thrips is indeed the pollinator then there certainly is no shortage of potential pollinators because the plants were well supplied with thrips. I would be really interested to hear from any reader who knows of an Alyxia ruscifolia that sets lots of fruit and is in flower now. It would be interesting to know if it also has lots of thrips and if so whether they are the same species as these.

(June 2012)

Alyxia ruscifoliaThis shrub with small prickly leaves grows to about 4 metres and is scattered across the Reserve but not in any great numbers. This year all the plants seem to be flowering profusely with their small clusters of perfumed white flowers. The arrangement of the bright orange fruit is quite distinctive with chains of up to four fruit looking for all the world like plastic beads strung together.

(June 2010)

This prickly understorey shrub is quite common in the reserve and very hardy and drought tolerant. The fragrant white flowers are produced in heads of from 3 to 5 flowers on the ends of the branches. The fruit is an orange berry about 10 mm in diameter which is produced singly or in a chain of up to 4. This plant together with the Pittosporum multiflorum are very useful understorey plants as replacements for the Ochna.

(August 2007)

Advertisements