Horneophyton
sporangia
Horneophyton,
one of the early land plants preserved in the Rhynie chert, has often
been described with drawings far off reality, as already mentioned in
Rhynie
Chert News 15 . So
it may be appropriate to show a few more details here.
Certainly
the sporangia are not shaped as shown in an often reproduced schematic
drawing [1] but it is not easy to produce a more typical one
since
the shape can vary greatly.
There is one feature
which is characteristic for Horneophyton:
It is a kind of column inside the sporangium, called columella. It may
be forked or branched, with every branch belonging to a protrusion of
the complex-shaped sporangium.
What is seen in Fig.1 is either a simple-shaped
sporangium with uncommonly short and thick columella or
part of a more complex one.
The obtuse angle between the two sporangia in Fig.2 may be compared
with such angle on a forking columella as, for example,
in [2]
or RCN 15,
Fig.5. There may have been a common cause in either case. It is
thinkable that forking or multiply branched sporangia evolved from
adjoining sporangia as in Fig.2 by fusion.
Fig.1: Horneophyton
sporangium, or part of it, with broad columella. Image width 4.3mm.
Fig.2 (below): Horneophyton
sporangia, adjoining, with broad columellas.
Image width 7mm.
The baroque shape in Fig.3 is apparently due to
shrinkage of the wall of the empty sporangium.
Fig.3 (below right): Horneophyton
sporangium of uncommon aspect, empty.
Image height 5.5mm, same scale as Figs.1,2.
Fig.4 (left): Horneophyton
sporangium with spores,
60µm. Image width 1.7mm.
With
the higher magnification in Fig.4, the spores, 60µm, some of them still
stuck
in tetrads, are seen well preserved while the sporangium is in a state
of decay.
Well preserved spores of
Horneophyton
are also seen in [3].
Samples:
Fig.1: Rh11/61.3, Fig.2: Rh23/1.3,
Fig.3: Rh7/23.1, Fig.4: Rh13/14.1.
H.-J.
Weiss 2019
(Dec.)
[1] D.A.
Eggert : The sporangium of Horneophyton lignieri.
Amer. J. Bot. 61(1974), 405-413.
[2] W.El-S. El-Saadawy, W.S.
Lacey: The sporangia of Horneophyton lignieri
..., Rev. Pal. Pal. 28(1971), 137-144.
[3] H. Steur:
steurh.home.xs4all.nl
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