Azolla arctica

Name

Azolla arctica

Rank

Species

Generic Name

[Genus] Azolla

Authors (Pub.)

Collinson M. E. Barke J. van der Burgh J. van Konijnenburg-van Cittert J. H. A.  

Publication

A new species of the freshwater fern Azolla (Azollaceae) from the Eocene Arctic Ocean [2009/5]

Journal

Review of Palaeobotany and Palynology

Volume

155

Issue

1-2

Page number

2

Year

2009

Parent Taxon

[Genus] Azolla

Fossil Status

sporae dispersae (megaspores & microspores)

Stratigraphy

Ypresian

Location

IODP Leg 302, Hole 4A, Core 011X, Lomonosov Ridge, Arctic Ocean

Paleoregion

Arctic

Data for Holotypus

Repository

Utrecht University, Laboratory of Palaeobotany and Palynology, Utrecht, The Netherlands

Repository Number

U22874

Num

pl. 1-3

Pub.

A new species of the freshwater fern Azolla (Azollaceae) from the Eocene Arctic Ocean [2009/5]

Diagnosis

Megaspore apparatus oblong with obtuse poles ca 350–400 μm long, ca 250 μm in maximum width. Megaspore inferred to be spherical to subspherical when uncompressed, 200–250 μm in diameter with a trilete mark at the proximal pole, laesurae extend up to two-thirds of the radius of spore, lips very slightly elevated. Entire megaspore apparatus covered with a thick (N8 μm) mat of intertwined hairs (0.3–0.6 μm in diameter) which arise almost entirely from the proximal region of the megaspore (hence suprafilosum). Remnants of megasporocarp wall, one cell layer thick, firmly attached over the proximal pole of the megaspore apparatus. Megaspore wall consisting of an exine ca 1–2 μm thick and a twolayered perine ca 3–4 μm thick. Megaspore surface finely rugulate under the transmitted light microscope. Under SEM and in thin section under TEM the inner surface of the exine forming a more or less continuous membrane beneath a more open structure; small irregular cavities dominating the exine and the endoperine, giving both a spongy, porous appearance; exoperine consisting of contorted nodular or clavate to tabular masses, (1–2 μm in thickness) with a solid exterior but alveolate interior, supported on sparse short narrow columns (usually less than 0.5 μm in width); exoperinal masses partially fused at different levels producing a rugulate undulating exoperine surface, finely and irregularly perforate, varying from punctate to foveolate, occasionally fossulate (maximum dimension of perforations 0.2–2.0 μm) and rugulae typically b1 μm in width). Occasional rare hairs extending fromthe exoperine (hence infrafilosum) into the distal parts of the megaspore. Exoperinal excrescences absent. Perine expanded in thickness and becoming spongy in structure near the proximal pole of the spore forming a collar; collar encircling the megaspore and giving rise to numerous hairs of the suprafilosum extending up into the central region of the float zone, and out onto the outer surface of the entire megaspore apparatus. Float system a compact dome-shaped structure occupying the apical third of the megaspore apparatus, extending over the apical part of the megaspore; floats numerous, 15 to 18, loosely organised in three tiers. Floats spongy, pseudovacuolated in structure, discoidal to spherical in shape and enmeshed by hairs of the suprafilosum. Microspore massulae single or grouped in clusters, irregular in shape with a thin outer wall, internally spongy, vacuolated in structure. Massulae contain up to 15 smooth walled trilete microspores (20–25 μm in diameter), laesurae extending up to two thirds of the radius of the spore. Outer surface of microspore massulae with numerous aseptate glochidia in two size classes, long glochidia N55 μm, shorter glochidia (b25 μm) often in bundles, each glochidium with a broad basal attachment, narrow lower stalk and broader upper stalk with a distal dilation and constriction below an anchor shaped tip, flukes narrow abruptly and lack recurved hooks.