Send your queries about plants to mailto:burnley-plantdirectory@unimelb.edu.au and we'll do our best to answer them.

1. What does "subsp." mean in the name Alnus acuminata subsp. glabrata?

   "subsp." is short for "sub-species". That is a variant of a species - a bit different, but not different enough to be called a species in its own right. In this case, this is a variant of the Andean Alder A. acuminata. "glabrata" means hairless, so I expect other forms of A. acuminata are hairy, and this one is different because it is hairless! We haven't seen any other subspecies of this species, so we can't be sure of this!

2. How big does the Evergreen Alder (Alnus acuminata subsp. glabrata) grow? What are its roots like? Can these trees be encouraged to have a deep root system by deep watering with dripper irrigation?

   These trees used to be sold in Australia under the name Alnus jorullensis, but thanks to some investigation at the Royal Botanic Gardens in Melbourne, we now know that was the wrong name for the trees we have been growing.

   What ever their name, they are trees that have some problems in Australia. All alders are trees that come from low-lying habitats, beside rivers and the like, in the Northern Hemisphere. They therefore are best in fairly moist, or even wet soils. This particular species is quite robust, and can survive some dryness, but can look very wretched without enough water.

   The general principle of deep watering to encourage deep roots is a good one, but many trees that come from moist habitats are naturally shallow rooted. This Alder has very vigorous and invasive roots, into the bargain! Tree root depth will also depend on the soil they are growing in. Is it deep enough for the roots to be able to grow to any depth? If it is a heavy clay, or is shallow, the roots will not be deep, because they need oxygen and space as well as water in order to grow.

   You could expect these trees to grow to 15m or more under average growing conditions in Melbourne. On the good side, they are fast, very tough in wet and heavy soils, and are quite attractive when growing well. They can make quite a good hedge, but need a lot of clipping as they are so vigorous. They don't appear to suffer from any major pests or diseases.

   In general it's a good idea in southern Australia to choose trees that can look their best with just rainfall, or minimal watering at the most. (We are still very low on water, despite the recent rain!)

3. I can't find some of the plants in my garden in the Burnley plant directory. The plants I want to know about are:

   1. Shad bush
   2. Hydrangea maulata    It looks like Hydrangea aspera on the directory but grows upright.
   3. Geranium maderense
   4. Silene

   
   You won't necessarily find all the plants in your garden in the Burnley plant directory - it has 1206 species, but there are lots more! (The next edition will have another 500 or so; we hope it will be out in around 12 months.)

   1. Shad bush

      The problem here is the common name! This plant is probably Amelanchier canadensis. We have the common name "Snowy Mespilus" in the Directory. Thanks to your enquiry, I have added "Shad Bush" as a common name for the next version, so future searchers will find that name.

   2. Hydrangea maulata    It looks like Hydrangea aspera on the directory but grows upright.

      Hydrangea maulata - could be H. maculata. The common hydrangea is H. macrophylla. There is a cultivar H. macrophylla 'Maculata'. 

      Hydrangea aspera in the Burnley gardens grows quite upright, too. It can depend where it is growing (amount of shade), and how it is pruned. It has narrow, rough-surfaced leaves, compared to the broad, smooth leaves of H. macrophylla.

   3.  Geranium maderense

      Geranium maderense is not in Version 1 of the Directory, but will be in the next version - we have the pictures ready to go! It is a wonderful plant that comes from Madiera, as the name maderense suggests.

   4. Silene

      A couple of species of Silene are commonly grown. The Burnley plant directory has Silene dioica, but Silene pendula is commonly grown, too. It is an annual, whereas S. dioica is perennial. They are members of the Carnation family, and have attractive pink flowers

4. Name changes in the eucalypts: A recent reader asked about a name change she had heard of for the Red-flowering Gum, which was formerly called Eucalyptus ficifolia. She also wondered how the new genus Corymbia can be distinguished from its close relatives Eucalyptus and Angophora.

   The red flowering gum tree is now named Corymbia ficifolia. Some other trees that we commonly grow in Melbourne (Lemon-scented Gum and Spotted Gum) are also now in this new genus, becoming Corymbia citriodora and Corymbia maculata instead of Eucalyptus.

   It is easy to distinguish an angophora from a eucalypt. If you look at the way the leaves are arranged on the stems, you will find that eucalypts have their leaves borne singly, and, if you inspect the stem, you'll notice that the leaves spiral up the stem. Angophoras have their leaves in pairs, opposite each other on the stems. Only a very few eucalypts bear opposite leaves, although many have leaves that are opposite during the juvenile phase.

   The fruit of the two genera are different also: while quite similar, Angophora fruit always have ribs on the outside, extending into little teeth that project above the top of the cup-like capsule. Eucalypt fruit don't have these ribs. The most common angophora in Victoria is Angophora costata. It has patchy-smooth bark which often has red colouration through it. If you find one, look for the fruit - they are very distinctive and will enable you to identify any Angophora species (there are only about 5).

   Corymbia is not quite so easy. These trees have alternate leaves like the eucalypts, and smooth fruit with no ribs. The fruit is like a cup, but narrows in at the top in a shape that is described as "urn-shaped". If you look at the capsules of Corymbia ficifolia, you'll see what I mean. You'll find that the fruit of Lemon-scented Gum and Spotted Gum are smaller, but similar in shape.

   Trees in the genus Corymbia also have their flowers borne in a different way from other eucalypts. This can be less easy to spot, but typically the flowers are borne in quite large branched clusters (known as "corymbs", hence the name Corymbia). These clusters are often borne on the outside of the canopy, which makes them showier in flower than most of their eucalypt relatives.

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