Isactis centrifuga Bornet ex Collins

• Region

  North America

• Country

  United States of America

• State/Province

  Rhode Island

• County/Municipio

  Newport Co.

• City/Township

  Newport

• Locality

  Ochre Point, on soft crumbling rocks at low water mark

• Coordinates

  41.4709, -71.2989

• Coordinate Uncertainty (m)

  495.369

• Georeferencing Method

  Georeferencing Quick Reference Guide, Version 2012. Located coordinates on shore closest to geogr. center of Ochre Point. Measured from selected coordinates to farthest extent of the point to find linear extent (483.80 m). Input information into MaNIS Georef. Calc. to find uncertainty radius.

• Geodetic Datum

  WGS84

• Distribution

  Map all specimens of this taxon

0 1

cm

7 8 9 10
copyright reserved

The New York
Botanical Garden

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Isactis centrifuga Bomet ms. Collins,

Rhodora 2: 1$6* May 1901»

Frond dark green or nearly black, up to 4 cm. diameter, growth marginal, the
central portion of the frond becoming detached from the substratum and rounding
upwards, while the margin remains closely attached. Filaments 8-12.«. diam«, slight-
ly swollen at base, reaching a length of a millimeter; sheath firm^usually trans-
lucent, sometimes brownish and opaque; trichomes 8-10yu. diam«, cells one third to
one half as long as wide; heterocysts basal, spherical or depressed; rarely inter-
calary, spherical or elongate. On rocks near low water markp Ochre Point, Newport,
R. I., May 26, 1900— Dr. E. Bomet in litt.

This plant was at first supposed by the writer to bo Rivularia Polyotis
(J. Ag«) Bom. ¿j Flah., YThich might be expected on our coast; but on submission

oj. spec liens to Dr. Bomet, the latter pointed out the distinctly marginal growth
of the frond, which would refer,it to the .genus Isactis. This genus has hither-
to been monotypic, X. p.Iaim (Harv.) Thuret, growing on algae, shells and stones,
being found in the Mediterranean and in the warmer waters of both sides of the
North Atlantic. From this well known plant 1» centrifur.a differs by the thicker
frond, larger filaments and trichomes, and especially by its character of loosen-
ing itseli xrom che substratum at the centre, while the margin continues firmly
attached and growing; soiiaetimes the older parts are broken away leaving only a ring.

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Phycotiieca Boreali-Americana. Collins, Holden, and Setcbell.

757. Isactis centrifuga Bomet.

On soft crumbling rocks at low water mark, Ochre Point, Newport^
Rhode Island, June 10, 1900.

F. S. COLLINS.

The description of this species will be published in Rhodora for
Feb., 1901.

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Determined by Francis Drouet	ÌV. ISTI

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