Fascinating Lichens of Sri Lanka

Stereocaulon
Foam lichens, Easter lichens
Lecanorales Stereocaulaceae
125
Physciaceae
Fr
VR
IC
Siphula decumbens
Description Fruticose. The thallus is whitish grey, broad, and with lobes that
are frequently dorsiventral with one side more markedly scabrid (rough with
irregular, delicate projections), irregularly branched and lobed in several planes,
attached to the substrate by a rhizine like rooting system, fragile and erect.
Medulla is solid. This is a sterile species.
Chemistry K+ bright- yellow turning brownish red.
This species is varied significantly over a range of habitats, exhibiting considerable
morphological variation.
Stereocaulon cosmopolitan genus found mainly on rocks and soil commonly
mixed with mosses covering large areas of soil or rocks. Species of Stereocaulon
produce cephalodia (brown and pink-purple structures seen on the following
photos included under this genus), that are important in the nitrogen cycling
of habitats. Cephalodia are structures which form on the surface or inside of a
lichen thallus, containing cyanobacteria as a secondary photobiont that fixes
nitrogen.
So far, six species are known from the upper montane habitats of Sri Lanka.
Recent work carried out in the Nuwara Eliya District, led to the discovery of one
species that is a new record for Sri Lanka by Weerakoon and Aptroot (2014) which
was previously only known from high elevation sites in Sikkim - India. The two
species included here were found in montane open soil banks in Nuwara Eliya,
and have restricted distribution in montane areas. Further field studies in similar
habitats in the upper montane regions of Sri Lanka are required to estimate the
total diversity of this genus.
This genus includes dimorphic fruticose lichens, with a granular to squamulose
horizontal primary thallus that is disappearing in most species. The secondary
thallus is vertical and fruticose. The branched stalks are generally seen in thick
clumps or tight cushions and attached by a basal holdfast.
Stereocaulon replaces reindeer lichens (Cladonia) as the dominant ground cover
in some parts of the boreal forest. In these regions, it becomes an important
component of the caribou winter diet. Some species of Stereocaulon have been
used as medicine in China and India by mountainous tribal people.
Apothecia lateral or terminal, rounded, brown to black, central cone compact;
Asci: 4-8 spored; Spores: colourless, needle shape, elongate, 2-30 septate.
Chemistry cortex K+ yellow in all species, PD+ orange, KC-, C- or PD-, KC+ pink
or violet, C- in most species.
Stereocaulaceae
Status Very rare species. Can be easily spotted, as the species forms a conspicuous
grey colony among moss mats on well lit soil banks and logs. New record for the
Indian subcontinent and Sri Lanka.
Habitat Mostly restricted to humid high elevation forests above 1200 m to
1400m on soil banks and on few mossy logs.
Locations Few locations along the Pattipola Station to Horton plains.
Primary thallus; A
squamulose or
crustose thallus
from which fruticose
stalks or podetia
arise as secondary
components.
Podetia ; lichenized
stem- like portion of an
apothecium, this forms
the fruticose part of the
thallus, and apothecia
discs are absent. (Pseudopodetia=
Fake podetiate)
Phyllocladia; squamule
-like structure occurring
in Stereocaulon
150 Fascinating Lichens of Sri Lanka
Fascinating Lichens of Sri Lanka 151