North American species of Lactarius / L. R. Hesler, Alexander H. Smith.

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North American Species of Lactarius

Beginning with the least ornamented spores, in terms of the
light microscope, and progressing to more complex types, the spores
of L. subvellereus, L. vellereus, and L. piperatus all have similar, low
ornamentation. This type of ornamentation is about the least conspicuous of any in the genus and consists of low, small, crowded or more
usually widely spaced warts and wrinkles with a few thin to somewhat
coarser ridges and a very few connectives-the rugose type. The connectives usually form no more than a broken reticulum and the ornamentation is only about 0.2-0.3 p high. Kauffman (1918) reported the
spores of L. vellereus as being nearly smooth. The SEM photomicrographs indicate that the spores have low projections with many low
ridges and connectives giving a rugose appearance to the spore surface
similar to that of a Cortinarius spore to some extent. To judge by the
species studied to date, this rugose type of ornamentation is not common in Lactarius. Two lines of ornamentation patterns may be traced
from this type. The first leads to spores with distinct, isolated warts,
with few, if any, ridges or connectives. In the second, the ridges and
connectives are more prominent, leading to the development of various
types of reticulum.
From the rugose type of spore, spores like those of L. waltersii
differ primarily in that the warts and short ridges are slightly higher
and broader and thus appear more prominent. Connectives are occasionally present, but incomplete, so that no semblance of a reticulum
is visible in light-microscope studies. The best example, however, of
this pattern of isolated, discrete warts and particles of ornamentation
is found in L. deceptivus. In this species, the ornamentation consists
of isolated, blunt, slender conic warts, with only an occasional low
ridge or connective and never even a slight reticulum. The ornamentation
is about 0.77 to 2.0,u high. Kauffman (1918) termed these spores
echinulate; however, the projections are not acute like those found on
most Laccaria spores and thus the spores are not truly echinulate. The
plage region in L. deceptivus typically has a low, uneven, diffuse amyloid ornamentation. L. luteolus is another example of a species with the
tall, isolated particles of spore ornamentation in which there are few, if
any, connecting elements.
Progressing in the opposite direction, toward an increasingly reticulate type of ornamentation, L. neuhoffii and L. allardii should be
considered. In L. allardii, based on light microscope studies, the ornamentation is still low, as in the rugose type, but the ridges and connectives are somewhat more noticeable and an occasional mesh may
be observed. If one then examines spores of L. neuhoffii, the ridges
and connectives are clearly an important part of the ornamentation
pattern and the spores are considered to have a broken to partial
reticulum. The difference in spore ornamentation between L. neu