Sunday, March 31, 2013

Recent Mushrooms - late March

Bark Mycena - Mycena corticola

Finally a few warm days, and then some rain.  These minute Bark Mycena's were fruiting on the sides of some White Pines.

That's it for the first "Recent Mushrooms" post of 2013.


Monday, March 25, 2013

When do Red Oak Leaves Drop

Red Oaks (Quescus spp.) are one of the few deciduous trees in MN that hold onto to their leaves throughout the winter.  So when do they drop them?  The short answer is "In the spring".  But I'm curious and would like to know with a bit more precision, so I intend to keep an eye on a couple of Red Oaks in the following weeks to get more details.
Another related question is "Why do Red Oaks hold their leaves through the winter."  It could be that the leaves provide some protection for the buds against the cold.  Or the leaves drop in the spring to suppress the germination of other seedlings.  Or so they can provide a compost layer in the spring when it's most useful to the tree.  I'm not entirely convinced of any of these ideas.

An idea I like better is that the Red Oaks are somewhere in the middle in the evolution of the deciduousness (probably not a word, but I like it, sorry).  All trees loss leaves, just some do it more gradually, namely the confers (except Tamaracks, which are deciduous conifers).  The deciduous life style is a a relatively recent development in terms of the evolution of plants.  Perhaps the Red Oaks exhibit an intermediate form of it, somewhere between the more ancient conifers, and the rest of the relatively newer deciduous flowering trees.
The habitat of holding onto dead leaves, or other withered parts is termed marcescence.  The related American Beech (Fagus grandifolia, both in the Beech family, Fagaceae) also show marcescence.  Ironwoods (Ostyra virginiana) are also marcescent, but unrelated, being in the Birch family, Betulaceae.





Monday, March 11, 2013

Willow Witches' Broom


The dense clumps of twigs on this willow (Salix sp) are known as Witches' Brooms.  It's not a normal growth pattern, but is caused by a type of bacteria known as a phytoplasma.
It seems not much is known about phytoplasms.  Here's what I have gathered, mostly from the U of MN extension service.
  • They are extremely difficult or impossible to culture outside of their host organism.
  • Their presence does interfere with the health of the plant.
  • Most are unidentified to species or genus.
  • There's probably a secondary host insect that spreads the phytoplasm to new trees.
  • Willows seem to be able to partion off the infected areas, leaving the rest of the plant uninfected.
  • It's not actually known for certain that Witches' Brooms on Willows in MN are caused by phytoplasms.
I see Willow Witches' Brooms on regular basis at Westwood Hills Nature Center.  It surprises me that something so conspicuous has so little know about it.