Research on tropical achlorophyllous, mycoheterotrophic
('saprophytic') plants with emphasis on morphology, anatomy, mycorrhiza and
ecology. Click here if you miss site navigation!
are puzzling! They are always characterized by remarkale reductions concerning root,
shoot and leaf structure and sometimes even hardly resemble a flowering plant. It is no
wonder that they are often collected by mycologists! Here some basic information:
||Since assimilation of carbohydrates through photosynthesis
without chlorophyll is impossible (as far as we know) and the direct metabolization of
dead organic material has never been detected in flowering plants, achlorophyllous plants
must have another source of carbon. They split up in two distinct groups:
- These plants develop special organs (haustoria) penetrating foreign plant tissue in
order to participate at least to some extend from their host's assimilates (carbon
compounds), water or nutrient uptake (e.g. Dodder, Broomrapes).
- Mycoheterotrophic Plants ('Saprophytes')
- In these plants a fungus (or several?) lives inside their roots ('mycorrhiza')
providing all requirements for plants growth. This is the plant group that I
Voyria truncata just emerged upon the soil surface. The pencil-sharpener
serves as a scale
|More than 400 species, in 87 genera and 11
families, of mycoheterotrophic plants have been described. Of those, only orchids and
members of the Monotropaceae (Indian-Pipe Family) are fairly well investigated.
Information about the other families are scarce. The most recent work on the neglected
genera has been done by Hiltje and Paul Maas and co-workers in
Utrecht/Netherlands. Nevertheless, root structures (morphology, anatomy, mycorrhiza) are
often entirely unknown. Most probably this is due to the remote and hardly accessible
habitat of these plants, the deep shaded tropical rainforest, and the fact that they are
easily overlooked in the field (see the picture to your left!). Hence, they get found by
Lately, I focused on the genus Voyria
of the Gentianaceae (Gentian Family) where 19 species have been distinguished so far, all
except one living in tropical America. Then I looked after Triuridaceae and Burmanniaceae (Triuris, Sciaphila, Burmannia, Dictyostega). Momentarily, I'm working on Burmanniaceae and Polygalaceae (Afrothismia, Epirixanthes). All of these plants share some morphological characters with Voyria but are not at all related to them. I could show that their
mycorrhiza is an arbuscular mycorrhiza (AM), a form of fugus-plant-symbiosis which is
very well known for more than hundred years. However, the achlorophyllous species so far
investigated revealed some very unique features, yet unknown despite the long and
intensive research on AM.
There are even more pictures on the page of Hiltje and
The results of my research so far are summarized in abstracts, available from my publicationlist. If you like to see some pictures, please visit the The Myco-Heterotrophs-Gallery.
My approach was led by the following questions. Answers I found so far are indicated
- What kind of morphological/anatomical adaptations have evolved in connection to
its special life form?
- At least one of those adaptations is a 'condensation' of the root system (becoming
short and thick).
- Are mycorrhizas in myco-heterotrophic species different from mycorrhizas in
- Yes, definitely in Voyria tenella, V. obconica, V. aphylla, Triuris hyalina,
and Afrothismia winkleri, less pronounced but still different in Voyira
truncata, Burmannia tenella, and Dictyostega orobanchoides. More strange
mycorrhizal patterns may be anticipated.
- Do the mycorrhizas between various myco-heterotrophic species differ?
- Yes they do, only in Voyria tenella and V. obconica I found the
same 'intraradical fungus garden'.
- What do mycorrhizal structures tell us about taxonomy and systematics?
- The closely related Voyria tenella and V. obconica do have the same
mycorrhiza whereas V. aphylla shows an intermediate pattern, linking to the
mycorrhiza of V. truncata and the autotrophic gentians. The two Burmanniaceae
Burmannia tenella and Dictyostega orobanchoides show at least in the
root cortices the same intracellular hyphal pattern. Afrothismia winkleri, a
Burmanniaceae from Africa, however, has an entirely deviating mycorrhizal pattern
(although it is an AM!).
- How do these plants use their root fungus?
- Very sophisticated!! Please read the abstracts e.g. on Afrothismia winkleri and Voyria
- What is the actual carbon source?
- From the observed direct hyphal bridges between roots of neighboring plants and the
achlorophyllous plants we must infer the carbon (and most probably everything else too)
must come from the neighboring plant.
Last revised on 18th of January 2001 by Stephan Imhof