Azolla jutlandica

Name

Azolla jutlandica

Rank

Species

Generic Name

[Genus] Azolla

Authors (Pub.)

Collinson M. E. Barke J. van der Burgh J. van Konijnenburg-van Cittert J. H. A. Heilmann-Clausen C. Howard L. E. Brinkhuis H.  

Publication

Did a single species of Eocene Azolla spread from the Arctic Basin to the southern North Sea? [2010]

Journal

Review of Palaeobotany and Palynology

Volume

159

Page number

155

Year

2010

Parent Taxon

[Genus] Azolla

Fossil Status

sporae dispersae (megaspores & microspores)

Stratigraphy

Eocene

Strat. comment

Lillebælt Clay Formation

Location

Kirstinebjerg, Trelde Næs, northern Lillebælt area, central Denmark

Paleoregion

Eurasia (Europe)

Data for Holotypus

Repository

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

Repository Number

U23047

Num

pl. 1, fig. 1

Pub.

Did a single species of Eocene Azolla spread from the Arctic Basin to the southern North Sea? [2010]

Diagnosis

Megaspore apparatus ovoid to pear-shaped, c. 350–410 µm long, c. 300 µm wide. Megaspore inferred to be spherical to sub-spherical with a flattened apical part when uncompressed, diameter c. 300 µm, trilete mark on the proximal pole, laesurae relatively short, extending up to one third of the spore radius. Laesurae slightly elevated, up to 5 µm high. Entire megaspore apparatus covered by a c. 5 µm thick mat of intertwined hairs (filosum). Hairs always arise from the proximal region of the megaspore (hence suprafilosum) but also, to a much lesser degree, from the exoperine of the megaspore wall (hence infrafilosum). Remnants of megasporocarp wall, one cell layer thick, firmly attached over the proximal pole of the megaspore apparatus. Megaspore wall consisting of an exine c. 4 µm thick and a two layered perine c. 7–8 µm thick extending to at least 15 µm with excrescences. Megaspore surface scabrate under the transmitted light microscope. 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. In thin section in TEM exoperine consisting of nodular to clavate masses (1 to 4 µm in thickness) with a solid exterior but an alveolate interior, supported on sparse short narrow columns (usually less than 1 µm in width). Exoperinal masses producing a surface which, under SEM, is scabrate, to granulate to baculate or clavate (units c. 1 µm in diameter and up to 2 µm high), to almost rugulate in places (units up to 3 µm in length). Sometimes hairs arise from the exoperine (hence infrafilosum) all over the megaspore. Megaspore perinal excrescences variable, ranging from 15 to 30 µm high, at irregular intervals over the spore, sometimes coalescing laterally; megaspores sometimes tuberculate. Perinal excrescences formed from proliferation of the endoperine and surmounted by exoperine. 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 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 pyramidal structure with rounded apex, occupying at least the upper two-fifths of the megaspore apparatus, slightly overlapping the proximal part of the megaspore. Floats probably 6, arranged in one tier, spongy, pseudovacuolated, wedgeshaped and enmeshed in the hairs of the filosum, organised in groups of two between partitions of a well-distinguished columella. Collar and columella originating from the exoperine in the apical part of the megaspore. Microspore massulae single or grouped in clusters, irregular in shape, internally spongy, vacuolated in structure. Massulae contain 6–20 smooth-walled trilete microspores (20–25 µm in diameter), laesurae extend up to one third of the radius of the spore. Outer surface of microspore massulae with numerous aseptate glochidia, from 25 to 40 µm long, with a broad basal attachment, narrower lower stalk, wider upper stalk with a distal dilation and a distinct constriction below an anchor-shaped tip. Flukes narrow gradually and lack recurved hooks.