AN EXAMPLE OF ANATOMIC STUDY OF EUCALYPTUS TO ASSIST SPECIES IDENTIFICATION: FROM ORGANISM TO ORGAN
   
             
       
Identifying eucalypt species can be a difficult task given the high number of species; variability between and within species, subspecies, varieties, provenances and cultivars; variability within a same tree at a certain sampling/observation time; variability of growth stages within a same tree along time... and the possibility of hybridisation. Observation of general tree habit (single stemmed, mallee, mallet), shape and size, colour and outlook of crown (presence of juvenile only, adult only or intermediate stages of foliage) and type of bark (several main types) in each main part of the tree are necessary as a first approach, and sometimes there is no need of a closer look to identify some distinctive species. But unfortunately (or fortunately depending on the point of view) in a majority of cases one has to go from the organism to the organ in order to identify a species properly. In these cases, if fortune helps, one can get samples of those key organs needed for a full identification:
   
             
       
   
     
Eucalyptus macarthurii / Botanical Plate / Lamina botanica
Eucalyptus macarthurii / Bark / Corteza      
 
 
Figure 1: Initial approach to the tree, observing bark type, colour, texture and shedding form. Later approach to mature leaves to observe size, colour on both faces, branchlet type and presence or absence of reproductive organs in any stage of development.
 
 
Eucalyptus macarthurii / Flowers and Fruits / Flores y Frutos  
           
   
Figure 3: Photographic record of key organs, including (if available) juvenile, intermediate and mature leaves prefferably attached to branchlets; samples of inflorescences allowing easy counting and estimated size measurement , preferrably complete clusters including peduncles, pedicels and branchlet pieces; and samples of infrutescences allowing easy counting and measurement, again preferrably complete and attached to branchlets.
 
Figure 2: Detailed inspection of reproductive organs present, trying to find if available for sampling several flower buds and several capsules, collecting amounts of any of them in each stage of maturity present in the tree.
     
               

SAMPLING, MEASURING AND ASESSING KEY ORGANS FOR SPECIES IDENTIFICATION
 
0 - Scale: Prefferably an object allowing an objective and easily recognisable size assessment. A transparent ruler both in inches and centimetres would be ideal.

1&2- Inflorescences and infrutescences: Normally the key element to allow a good identification of an Eucalyptus species, or to narrow the possibilities to a reduced number. Important details are:
- Number of flower buds per inflorescence (better if an average on half a dozen sampled inflorescence clusters). Sometimes they are in higher number than capsules (some buds are not pollinated or do not reach blooming stage).
- Number of capsules per infrutescence (better if an average on half a dozen sampled capsule clusters). Many times, especially in almost ripe or rippen capsules, several capsules are missing. In such cases careful observation of number of scars left by pedicel abscission still allows to account number of capsules per cluster.
- General shape of both buds and capsules, and for the later, position of valves (inserted, rim level or exserted).
- Flower bud insertion on cluster (presence or absence of pedicels, and length in case of presence).
- Inflorescence insertion on branchlet (presence of absence of peduncles, and length in case of presence).

3- Juvenile foliage: For many species it is highly distinctive due to less common shapes than those sickle-shaped ones normal in adult foliage. Juvenile leaves are normally opposite and lack of petioles (they are inserted directly on branchlets). Intermediate leaves start changing shape to the adult form and grow over short petioles that become larger as the tree matures. Juvenile leaves are not to be confused with new growth leaves, which are present (be it as new juvenile or as new adult leaves) at any age and can also sometimes help identification. Important details are:
- Type of insertion of branchlet, shape (paying attention to the base of the leaf near insertion), size, leaf margin (crenulate or not), leaf vein angle, degree of similarity of colour on both faces, presence or absence of waxes.

4- Adult foliage: For some species it is highly distinctive too but the most common case is it being sickle shaped. Adult leaves are normally alternate and have petioles of varying length. However they still are important assistance to identification for some species so in addition to the parameters mentioned for juvenile leaves special attention is to be put on:
- Presence or absence of inflorescences or infrutescences in axillary position (growing or not on the junction point of branch and petiole).
- Presence or absence of obliquity (degree of symmetry of the base of leaves where joining petioles).

5- Leaf venation and essential oil glands: Far less distinctive for many species, it still can add some evidence to help clarify special cases. Not prioritary and requires using al light source to assess parameters as type of reticulation of leaf veins and degree of abundance of oil glands.
       
   
 
   
IS THIS ALL FOLKS?
 
       
   
At this point one could think "hey, with this all we are able to identify them all". Wrong. If we already went from organism to organ, for some species a further travel is necessary. That is where we go from organ to organillo. From all the organs mentioned above, those which help most to identify an eucalypt are fruits (capsules) and flowers. But this is not only true when observing with the naked eye. It is precisely inside of flowers where some small organs and their shapes, sizes and numbers can help to work out which eucalypt we are dissecting. But this is a difficult microscopic trip for another day!
   
   
 
       
    FROM ORGANISM TO ORGAN :: FROM ORGAN TO ORGANILLO :: FROM ORGANILLO TO TISSUE :: FROM TISSUE TO CELL :: FROM CELL TO ORGANELLE :: FROM ORGANELLE TO DNA