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96 FERNS OF NORTH AMERICA.
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The sori are placed one on each veinlet, — on the upper veinlets
near the margin of the lobes, but near the middle of the lower
veinlets ; thus forming a very evident intramarginal line around
the lobes of the pinnæ, and descending pretty near the midrib
between the lobes.
The indusium is far more rigid and persistent than in most
of our other A s p id ia : it is roundish-reniform, and commonly
quite smooth, though Mettenius says “ tenuiter pilosum.” In the
other variety the indusium is densely setose. The spores are
bean-shaped, and often have a deeply-impressed hollow on the
concave side. Their surface is very minutely roughened.
This tropical fern has been known since the beginning of
the present century ; but it was first discovered within our limits
in 1873, when Mr. C. E. Faxon collected it near Enterprise,
Florida. In the genus Aspidnnn it finds a place in the section
Nephrodium, as this group was understood by Schott, and defined
by Presl (Tentamen, p. 80) and by Moore (Index F il, p. Ixxxvi.).
In the Species Filicum and the Synopsis Filicum it is \E im e -
phrodimn of the genus Nephrodium. The group, by whatever
name it is called, consists of those Aspidioid ferns which
have a reniform indusium, and simple pinnate veins, of which the
lower pair or several pairs of contiguous lobes unite at an angle,
and send out a ray or veinlet to the sinus. There arc in the
world about fifty species referable to the group, nearly all of them
inhabitants of tropical or sub-tropical climates. Aspidhim molle,
which may possibly occur along the Gulf shores of our Southern
States, belongs near the present species ; but, if it should be found,
FERNS OF NORTH AMERICA. 9 7
it can be readily distinguished by its softly pubescent frond and
shortened root-stock.
Dr. Mettenius seemed to be confident that his var. glabrum
was the Polypodhtzn unitum of Linnæus ; but Mr. Baker remarks
that the Linnæan specimen so named is the Aspidium cucullatum
of Blume and Mettenius. Should this view be finally adopted, it
would seem proper to call the present fern by the name assigned
to it by Schkuhr, slightly modifying the orthography, so as to
correctly represent in Latin letters the Greek word which
means roundish, and was evidently intended by Schkuhr to refer
to the roundish lobes of the pinnæ.
The synonymy of both forms of this species is very much
involved, and perhaps will never be entirely cleared up. Ampler
synonymy may be found in Flooker’s Species Filicum, and in Dr.
Mettenius’s account of Indian and Japanese ferns, in the Annals
of the Leyden Botanical Museum.
Plate X I II. — A frond of Aspidium unitum, var. glabricm, with the
nearly naked elongated root-stock. A pinna, slightly enlarged, shows the
position of the fruit-dots ; and in two lobes, enlarged about six diameters,
the peculiar venation is well exhibited. The indusium, with its sinuous-
margined cellules, is highly magnified.
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