Eucalyptus flowers: the case of paired inflorescences


When Eucalyptus behave strange: flowers that do not follow the usual pattern

Gustavo Iglesias Trabado Contact GIT Forestry Consulting
GIT Forestry Consulting - Consultoría y Servicios de Ingeniería Agroforestal - www.git-forestry.com - EUCALYPTOLOGICS

Double flowers: why?

Observe any new growth in your eucalypts, where the smallish new leaves are starting to form. You can see there that near the base of a pair of leaves (if juvenile and sessile) or near the petiole of adult leaves, in the axil, new small branchlets in development that will become soon new lateral branches.

Eucalyptus globulus Eucalyptus pulverulenta Eucalyptus neglecta paired inflorescences Eucalipto blanco Eucalipto de hoja de corazón Eucalipto neglecta flores pareadas Galicia Spain España Marennes Francia Mt Annan New South Wales Australia Phil Sydney Benoit Binson Marennes GIT Forestry ConsultingFig. 1: Examples of paired inflorescences in three Eucalyptus species

This new growth is happening from an axillary bud, near the location of a joint between a leaf and a branch. It normally becomes a new branchlet if it is a vegetative bud, which happens all along the life of the eucalypt, and it becomes an inflorescence if it is a reproductive bud, which happens when the plant reaches reproductive maturity.

The issue is that this tissue that is dividing into new cells (hence growing) is not "unique". Buds can develop "more than once in the same axil". That is why you can have a new leaf first, and an inflorescence later, growing from the same axil. This is the most common case in Eucalyptus (not in Corymbia) and the reason for inflorescences being defined as axillary. In this case, the first bud is vegetative and the second bud is reproductive.

But in the pictured examples we are seeing something a bit of unusual, which is paired flower clusters. It is not the "common thing" but it can happen and the reason seems to be physiologic. Sometimes the plant "decides to produce flower buds" more than once in the same axil. So you can have more than one reproductive bud later developing flower clusters in the same axil instead just of 1 vegetative (new leaf or branchlet) + 1 reproductive (new flower cluster). As the examples above depict, you can have 3 buds from the same axil, 1 vegetative (new leaf or branchlet) + 2 reproductive (2 new flower clusters). When happening, this variation normally affects just a small number of axils per plant.

Taxonomic implications

For E. globulus ssp. globulus, which normally produces only one flower bud per axil, this situation can be confusing because flower buds (and later seed capsules) are big sized and almost sessile (no clear peduncles). When a specimen of this subspecies "decides to produce paired inflorescences" it can be mistaken with "E. bicostata" (Eucalyptus globulus ssp. bicostata, which regularly produces flowers in groups of three).

Eucalyptus bicostata Eucalyptus globulus ssp. bicostata flower buds Eucalipto bicostata inflorescencia flores Mt Annan New South Wales Australia Phil Sydney GIT Forestry ConsultingFig. 2: Example of E. bicostata flower buds collected at Mt Annan (NSW, Australia). Bud clusters are regularly grouped in 3's and smaller sized than in E. globulus ssp. globulus.

Some literature suggests this paired inflorescence feature can become a factor to identify other species but we are of the opinion some caution is needed when botanising samples since if this is a physiologic response it could happen in many other species. What would matter then is a careful inspection of botanical samples in order to identify which is the frequency of paired inflorescences in a certain flowering branch.

It is good keeping photographic record if you observe it in any eucalypt species. It is a curiousity!! Also, there is no need to say it will make a massive bunch of flowers, double the size of a normal cluster, which deserves even more photography.

Contact GIT Forestry Consulting / Contact Eucalyptologics / Contacto GIT Forestry Consulting / Contacto Eucalyptologics / Lugo, Galicia, Spain, EspañaContact GIT Forestry Consulting - Eucalyptologics

If you observe this feat in any eucalypt around, do not be hesitate contacting us and share the photos!


Special thanks to Benoit Binson at Marennes (France) and Phil in Sydney (Australia) for their photographic contributions.

You can visit Phil's Blog "Eucalypts In Habitat" for some great views on NSW eucalypts.

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© 2007 Gustavo Iglesias Trabado. Please contact us if you want to use all or part of this text and photography elsewhere. We like to share, but we do not like rudeness.

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