Pouch, secotioid, or sequestrate?Posted: 17/05/2013
I was doing honours degree the year that the 13th International Botanical Congress was held in Sydney in 1981. Many foreign botanists and mycologist passed through New Zealand either on their way to the Congress or on their way home. One of these was Harry Thiers (Thiers and Halling 2003) who gave a presentation at Victoria University of Wellington on his research into secotioid fungi.
This group of fungi had for a long time been called tobacco pouch or pouch fungi. It obviously made sense way back when as tobacco pouches were common objects but in 1981 I had no idea what one was. It was wasn’t until the age of the internet that I saw that they were often small draw string bags that closed and created a pleated pouch very much like the form of this group of fungi. Here is an example of a linen tobacco pouch used by German soldiers during World War I which rather than a draw string has a brass ring to close it.
However by the 1950s it was realised that there were a group of pouch fungi that clustered, at least in their gross morphology, around the genus Secotium in the family Secotiaceae. Researchers such as A.H.Smith and Rolf Singer began to refer to them as secotiaceous and then secotioid fungi which simply mean Secotium-like. Secotium is from Greek and refers to the chambered internal flesh (the gleba). I have likened it to the appearance of aero-chocolate.
Unfortunately names have a limited life and in 1992 Kendrick introduced the term ‘sequestrate’ for this grouping. It refers to the sequestered or hidden away spores which can only be released when the fruitbody rots or is eaten.
During this time it was realised that the members of the sequestrate fungi were not closely related to each other but more closely related to normal mushrooms based on spore characteristcs. Thus the sequestrate genus Secotium has similar spores to the mushroom genus Agaricus, and Thaxterogaster has the same spore form as Cortinarius. The big question was which way had evolution proceeded? Was the sequestrate form the ancient form with the aero-like gleba evolving into gills or did the aero-like gleba represent the failure of gills to develop. The general consensus today is that the sequestrate form has evolved from the mushroom form by the fusion of gill tissue to form a gleba and the loss of a mechanism to flick spores into the air.
There are two interesting things to consider about sequestrate fungi. The first is that a great many species can be found in the dry eucalypt forest and the desert of Australia. This has led to the idea that the sequestrate form has evolved to protect the gills and the forming spores from dehydration and death by keeping them enclosed in the moist gleba.
The second thing is the loss of the ability to release spores which has been compensated for by the sequestrate fungi being very attractive food for animals and in particular mammals. Some very interesting work has been done in Australia to show the importance of potoroos and bettongs, small herbivorous marsupials, in the dispersal of these fungi (Lepp 2012). This is mirrored on other continents where rodents such as squirrels gather and hide sequestrate fungi. Many of these fungi are not colourful and have scents to attract the mammals.
But this leaves a big question, New Zealand is not dry and does not have any native mammals so why do we have so many species of sequestrate fungi? One possibility is that despite there being plenty of water New Zealand vegetation suffered from physiological drought during the long period of glaciation of the ice ages. For instance during the last glacial maximum 21 thousand years ago much of New Zealand was was dominated by cool grasslands and shrublands with only small isolated forest pockets. It could easily be imagined how sequestrate forms would evolve to cope with these cool conditions.
However the problem of spore dispersal persists as there were no mammals. As noted above many of the mammal dispersed sequestrate fungi are not colourful. This is in stark contrast to the New Zealand species which are brightly coloured. This led Ross Beaver (1993) to suggest that these were typical bird attracting colours and that birds might be the dispersal agent for the spores. He suggested that these fungi were mimicking fruits and berries and here is his photo of Weraoa erythrocephala with the fruits of supplejack (Ripogonum scandens) and miro (Prumnopitys ferruginea).
Given that no bird species living in New Zealand are known to eat sequestrate fungi Ross speculated that it might have been the now extinct large, flightless ratites, the moa, that inhabited New Zealand up until fairly recently.
Usually when I tell this story I finish by saying that while it is an interesting story we can never know the answer without a living moa to observe. Then a few months ago I saw the following picture of the Queensland ratite, the cassowary (Casuarius casuarius), feeding on quandong fruit (Elaeocarpus angustifolius).
The quandong fruit look like Thaxterogaster (Cortinarius porphyroideus) so it becomes easy to imagine moa being attracted to them and acting as the spore disperser.
Beever, RE 1993. Dispersal of truffle-like fungi in New Zealand. In Hill RS Southern Temperate Ecosystems: Origin and Diversification 22. Hobart, Australia.
Kendrick, B. 1992. The Fifth Kingdom. 2nd Edition. Mycologue Publications, 8727 Lochside Dr., Sidney, BC V8L 1M8, Canada.
Kubasik M 2013. Pommersches Pionier Bataillon Nr. 2. http://pommerschespionier.com/index.php/collection/various/tobacco-pouch/
Lepp H 2013. Australian fungi: fungal ecology: fungi and vertebrates. Australian National Botanic Gardens and Australian National Herbarium, Canberra. http://www.anbg.gov.au/fungi/ecology-vertebrates.html
Newnham R, McGlone M, Moar N, Wimhurst J, Vandergoes M 2012. The vegetation cover of New Zealand at the last glacial maximum. Quaternary Science Reviews. In press.
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TerraNature Trust 2010. New Zealand ecology: flightless
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Ziegler C 2013. World Press Photo competition
2013, Nature, 1st prize singles, Christian Ziegler. http://www.worldpressphoto.org/awards/2013/nature/christian-ziegler