Monday, February 13, 2017

winter alders

Cones and seeds of Alnus cordata (left) and Alnus glutinosa (right)

Alnus cordata, the Italian Alder, native to two quite small areas in Corsica and southern Italy. But now introduced everywhere as the handsomest of the alders; with the same year-round interest as the others, but not so dependent on moist soil; upright, happy and neat in urban street plantings. Bigger cones and a more open crown than our other alders. Winged seeds.

Alnus glutinosa, the Common, European, or Black Alder. Native trees are usually by water, but they can be planted elsewhere. Winter branches crowded with last year's cones and next year's catkins. Winter crown can look dark purplish from a distance. The cones are much smaller than those of A. cordata. The seeds are a pretty red-orange colour. They're winged, and air is trapped within the wings so they also operate as swim-bladders, handy for spreading the seeds down a stream.

*Some people deplore the word cone when talking about alders, because alders are not conifers, and some people use the word strobile or strobilus, but this is no more correct than cone, since it really refers to a spore-bearing structure such as the fertile tip of a horsetail. Alders are true flowering plants and these are seed-bearing structures.

Botanically, one ought to call the  female "cones" pistillate catkins and the male "catkins" staminous catkins. They're variations of the same basic structure. But common English usage dictates that the word "catkin" can only be used during the flowering phase. When we're talking about the much longer fruiting phase, the only real alternative is "fruit", which is unspecific at best. So "cone" it is.

Alnus cordata (Italian Alder)

Photo from December 16th, 2016 -- before the last of the leaves fell.

Alnus cordata debris, Swindon, 23rd February 2017

What the walkways looked like, after a gusty night on the margin of Storm Doris.

Alnus cordata, male and female catkins (Swindon, March 9th, 2017)

Alnus glutinosa (Common Alder)

Typically crowded crown of the Common Alder. Photos from February 3rd, 2017.

Alnus glutinosa (Common Alder)

Alnus glutinosa (Common Alder)

Photo from February 3rd, 2017. Some early Common Alder catkins were already open, but not on this tree.

Alnus glutinosa, new cones starting out (20th February, 2017)

The same tree on 20th February. Close inspection reveals the reddish female catkins, much smaller than the male catkins (now fully open). These female catkins will become the cones.

Alnus incana (Grey Alder)

Winter crown of Grey Alder (Alnus incana). Often, this is more of a large shrub than a tree. Photo from February 11th, 2017. The new catkins were just opening.



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