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The clarification of the term 'hemiepiphyte'

5/5/2013

2 Comments

 
In a new viewpoint article, Professor Gerhard Zotz has clarified the use of ‘hemiepiphyte’ and proposed the rejection of the term ‘secondary hemiepiphyte’.

The current classification of canopy plants typically has three main groups: (1) holoepiphytes; (2) hemiepiphytes; and (3) climbing plants. Holoepiphytes are those that germinate and complete their life cycle on other plants. Climbing plants are vines (also called lianas) that require the structural support of other plants to reach the canopy; these can be further defined as herbaceous or woody categories. Hemiepiphytes are plants that have a root connection with the forest floor at some stage in their life cycle and can be further differentiated into primary and secondary categories:

  • Primary hemiepiphytes are plants that establish this connection to the ground after germinating in the canopy 

  • Secondary hemiepiphytes begin life on the ground, climb to the canopy and then lose their link with the ground. 

This is how the current classifications relate to each other (please note that this is my interpretation):
Current epiphyte classifications
Classification of hemiepiphytes has been confusing for many years – especially secondary hemiepiphytes (SH). Here is a conceptual picture of the difference between primary and secondary hemiepiphytes that I’ve drawn and below that, a list of problems with these classifications.
Hemiepiphye diagram
The problems:

As explained by Zotz (2013), there are multiple problems with the term ‘secondary hemiepiphyte’:

1.      Inconsistent use of SH has resulted in ambiguous application of the term and confusion over which species fit in this group.

2.      It is difficult to determine if any one species is a SH because although the main ground connection may be lost, adventitious roots can re-connect with the soil and these roots can be hard to find and trace.

3.      The term implies a close relationship with primary hemiepiphytes when there are in fact significant functional differences between the two groups, including: the location of germination; the growth form; the source of water and nutrients; and the structural support mechanisms.

A solution:

Zotz (2013) proposes that the use of the term SH is discontinued and that all climbing plants which germinate on the ground and possibly lose parts of their ground connection are instead referred to as ‘nomadic vines’. This change would achieve the following clarification:

1.      It should stop the ambiguous classification of canopy species and facilitate compatibility of data sets in higher-level studies. Also, the use of ‘primary’ with hemiepiphyte will be redundant and ‘hemiepiphyte’ will only refer to species that germinate on another plant and establish a connection with the forest floor.

2.      There will no longer be an implied functional relationship between the primary and secondary hemiepiphytes but instead the similarity of SH with vines/lianas will be highlighted

3.      Species that only sometimes lose their connection with forest soil will fit within ‘nomadic vines’. This new term can also accommodated the occasional germination of these species in the canopy.

This is how the proposed classifications relate to each other when based on the location of germination (please note that this is my interpretation):
New epiphyte classification
What are your thoughts? How does this new classification apply in New Zealand? Do you think any of our species can be classified as nomadic vines?
The roots of hemiepiphyte Griselinia lucida
The roots of hemiepiphye Griselinia lucida
2 Comments
Tahir Kamran
16/1/2021 02:25:49 am

Is G lucida native to New Zealand ?
You classification is very good but doesn’t tell which are stranglers ( out grow & kill host ) and which does live beside host .

Reply
Catherine Kirby
17/1/2021 12:21:11 pm

Hi Tahir,

Yes, G. lucida is native to New Zealand, see: https://www.nzpcn.org.nz/flora/species/griselinia-lucida/

We don't have any true stranglers in New Zealand. The only species that regularly forms a strong trunk of its own around the host tree is Northern rata (M. robusta) and it is generally thought that this species outlives the host rather than strangles it. By the time it germinates and grows up the mature host tree, that host is probably already many hundreds of years old. All other woody vines in NZ rely on the host for structural support. The rata would definitely affect the host tree but it doesn't strangle like the tropical strangling figs etc.

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    Catherine Kirby

    I work with NZ's native vascular epiphytes at the University of Waikato. I completed an MSc on epiphyte ecology and the shrub epiphyte Griselinia lucida and have recently published the Field Guide to NZ's Epiphytes, Vines & Mistletoes. 


    For me, the highlights of epiphyte research are the many unknowns, the amazing way that these plants survive in the canopy, and of course tree climbing!

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