Field and lab identification of Sphagnum is extremely challenging. I say this after three years of trying to get a handle on the ~30 species of the genus found in my region. Not only do you have to look at a number of features and do a number of preps, but often the character overlaps between species are such that you can be left hanging on an unresolved ID. In the WORST CASE SCENARIO when IDing Sphagnum, you might need to do the following steps:

Field Characters (Video One)
(1) Interpret the overall habit and growth form (Does it form loose, low-lying carpets, solitary sprigs, diminutive cushions, bulging hummocks?)
(2) Interpret colour-- while highly variable depending on exposure and hydration, among other things, some Sphagna are reliably red or brown or orange. Some are shiny when dry. Some plants are candy-striped.
(3) Consider the habitat (is it a forest species? Is it below the water line for most of the year? Is it along drainage margins? Is the habitat associated with calcaerous rocks of basic run off?)
(4) Determine the shape of the capitulum (Stellate? Flat? Hemispherical?)
(5) Search for the presence of and determine the prominence of an apical bud at the center of the capitulum.
(6) Are the leaves on the branches of the capitulum arranges in five tidy ranks around the branches?Do they come off at 90 degrees to the branch? Do they curve backwards as they dry?
(7) Are the branch leaves acute or obtuse, hooded ("cucculate") or fringed?
(8) Look at the plant side on to look for the pattern of emerging branches, both in bud form and in mature form further down the stem. How many branches are presence in each cluster and of those how many are growing outward ("divergent") and how many are hanging down ("pendant").
(9) What is the shape and orientation of the stem leaves? These are the leaves that come directly off the main stem. They are best seen by plucking off the capitulum and if neccessary the first few fascicles (clusters) of branches as you go down the stem. Are they triangular? Tongue-shaped?Appressed to the stem? Hanging down? Tattered?
(10) What is the colour of the stem? Red? Green? Brown? Pale? Variegated?
(11) Are sporophytes present? Some species carry them more reliably than others.

Microscopic Characters
To prepare sampled for the microscope I do the following steps.
(1) If specimen is fresh and wet, proceed to step 2, otherwise hydrate dried specimen by running it under tap water and rhythmically squeezing and releasing about 10-20 times while water runs. Slow route it to just let it sit in small tub of water for 30 minutes.
(2) Pluck off the capitulum, stain it, rinse it and press it under a slide to make branch and branch leaf cross-sections. Mount those to a slide in a drop of water, cover them with a coverslip. (Video 2)
(3) Pluck branch leaves from excess stained capitulum using tweezers and mount them to a slide. Some should be facing concave side up and some should be facing concave side down. (Video 3)
(4) Pull off fascicles to expose the stem and stem leaves. Stain a 1" fragment, rinse it. Pluck stem leaves with tweezers and put them on a slide in a drop of water with a cover slip overtop. (Video 4)
(5) Take remaining stem material and make 1 tangential section and 1 cross section. Put them on a slide in a drop of water with a cover slip overtop. (Video 5)
(6) delicately try to denute one of the stained branched of its leaves. Put it on a slide in a drop of water with a cover slip overtop. (impossible to make video of)

This takes about 2 minutes altogether and will leave you with the following:

• Branch Leaf Cross Section (Slide 1, Coverlip 1)
• Branch leaf whole mount upper surface (Slide 1, Coverlip 2)
• Branch leaf whole mount lower surface (Slide 1, Coverlip 2)
• Stem Leaf whole mount (Slide 2, Coverlip 1)
• Stem cross section (Slide 2, Coverlip 2)
• Stem tangential section (for surface cells, pores, fibrils) (Slide 2, Coverlip 2)
• Branch axis whole mount (for surface cells, pores, fibrils) (if you can keep track, Slide 1, Coverslip 2)

When all this is done, you will have everything you need to hopefully identify your Sphagnum using the Flora of North America Sphagnum key.

Posted on January 5, 2023 12:33 AM by rambryum