The Yorkshire Jurassic flora. II. Caytoniales, Cycadales & Pteridosperms. London: British Museum (Natural History)

214 Pages·1964·45.442 MB·English

by  Harris T.M.

THE YORKSHIRE JURASSIC FLORA
11. CAYTONIALES, CYCADALES & PTERIDOSPERMS
BRITISH MUSEUM (NATURAL HISTORY)
THE YORKSHIRE JURASSIC
FLORA
II
CAYTONIALES_, CYCADALES & PTERIDOSPERMS
By
THOMAS MAXWELL HARRIS, F.R.S.
Professor of Botany in the University of Reading
With seven plates
and sixty-seven figures in the text
LONDON
TRUSTEES OF THE BRITISH MUSEUM (NATURAL HISTORY)
Issued May 1964
© Trustees of the British Museum (Natural History), 1964
Printed and bound in Great Britain in the City of Oxford at the Alden Press
Collotype plates by Cotsu:old Collotype Co. Ltd., Gloucestershire
PREFACE
IT was originally intended to complete this work on the Yorkshire
Jurassic Flora in two volumes, but this has not proved feasible, and in
this second volume the author has limited his attention to the Caytoniales,
Cycadales and Pteridosperms, covering a total of fifty-two species be
longing to fifteen genera. It is hoped to complete the work on the remain
ing groups, the Bennettitales, Ginkgoales and Coniferales, in two further
volumes presently in hand.
As in the first volume, much of the material under examination has
been collected by Professor Harris himself and again the Department is
indebted to him for another important series of hand-specimens and slide
preparations, including type and figured material, which he has gener
ously presented to the National Collections. And once more, the very
informative figures in the text are from the author's skilful pen, this time
reinforced by seven plates.
To Mr. F. M. Wonnacott both the author and myself are yet again
indebted for the firm but discreet exercise of his editorial skill.
ERROL WHITE
Keeper of Palaeontology
CONTENTS
Page
INTRODUCTION I
SYSTEMATIC DESCRIPTIONS 2
CA YTONIALES 2
SAGENOPTERIS Presl 3
Sagenopteris colpodes Harris 4
0
Sagenopteris phillipsi (Brongniart) 8
CA YTON AN THUS Harris 13
Caytonanthus arberi (Thomas) I5
Caytonanthus oncodes Harris I7
Caytonanthus spo A I7
0
CA YTONIA Thomas 18
Caytonia sewardi Thomas 20
Caytonia nathorsti (Thomas) 22
Caytonia kendalli spo novo 24
0
AMPHORISPERMUM Harris o 28
Amphorispermum pullum Harris 28
CYCADALES and PTERIDOSPERMS 31
NILSSONIA Brongniart 32
Nilssonia tenuinervis Seward 33
Nilssonia thomasi spo nov. 37
Nilssonia sp. A 39
Nilssonia revoluta sp. nov. 40
Nilssonia syllis sp. nov. 42
Nilssonia tenuicaulis (Phillips) 46
so
Nilssonia compta (Phillips)
Nilssonia kendalli sp. nov. 55
ss
Nilssonia sp. B
DELTOLEPIS Harris 6o
Deltolepis crepidota Harris 6o
Deltolepis mitra sp. nov. 63
Deltolepis calyptra sp. nov. 63
PARACYCAS gen. nov. 6s
Paracycas cteis (Harris) comb. nov. 67
PSEUDOCTENIS Seward 70
Pseudoctenis herriesi Harris 72
Pseudoctenis locusta Harris 76
vii
Vlll CONTENTS
Page
Pseudoctenis oleosa Harris 78
Pseudoctenis lanei Thomas 82
Pseudoctenis sp. A 87
Pseudoctenis sp. B 87
Pseudoctenis spp. 89
CTENOZAMITES Nathorst 89
Ctenozamites leckenbyi (Leckenby) . 91
Ctenozamites cycadea (Berger) 95
Ctenozamites megalostoma sp. nov .. 99
Ctenozamites sp. A . 101
CTENIS Lindley & Hutton 102
Ctenis sulcicaulis (Phillips) 103
Ctenis reedi Harris 109
Ctenis kaneharai Y okoyama 112
Ctenis exilis sp. nov. II7
Ctenis cf. stewartiana Harris 121
Ctenis sp. 121
PACHYPTERIS Brongniart 121
Pachypte_ris papillosa (Thomas & Bose) 125
Pachypteris lanceolata Brongniart . 137
STENOPTERIS • 146
Stenopteris williamsonis (Brongniart) 147
Stenopteris nana Harris 151
Stenopteris nitida Harris 153
Unnamed Pteridosperms or Cycads 156
Cycad-like reproductive organs 156
ANDROSTROBUS Schimper 156
Androstrobus manis Harris 157
Androstrobus wonnacotti Harris 159
Androstrobus prisma Thomas & Harris 16o
Androstrobus szei sp. nov. 162
Androstrobus sp. A 163
BEAN IA 163
Beania gracilis Carruthers 165
Beania mamayi Thomas & Harris 168
Beania spp. . 169
Pteridosperm-like reproductive organ 170
PTEROMA gen. nov. 170
Pteroma thomasi sp. nov. 171
REFERENCES 179
INDEX 186
INTRODUCTION
As first planned, this volume was to include the Caytoniales, the Cycads, the Bennettitales and
various other Gymnosperms with leaves of more or less pinnate construction. This comprises
that vague assemblage often called the 'Cycadophyta'. However, the Bennettitales have been
excluded to expedite publication. I would like to take this opportunity to acknowledge the
generosity of Mrs. Hamshaw Thomas who placed her late husband's very large collection of
Yorkshire fossils at my disposal. The new specimens have made it possible for me to reorganise
the descriptions of several species and numerous specimens of his are figured here.
ToM M. HARRIS
SYSTEMATIC DESCRIPTIONS
Class Caytoniales
This isolated class is still no more than an isolated genus and this genus has still no name,
though it has been called 'The Caytonia plant' for informal purposes. It is better with no name
because however strongly supported it is essentially an inference rather than a fossil. The
separate parts are named, the leaf being Sagenopteris, the fruit and seed being Caytonia and
the microsporophyll being Caytonanthus. Dispersed pollen agreeing with that of Caytonanthus
has been described under the names Alisporites Daugherty, Vitreisporites Leschik and Caytoni
sporites Couper. Since other plants also produced pollen of this general type it is unsafe to
identify dispersed grains as Caytonialean.
The affinities of the Caytoniales have from the first been regarded as open. Thomas ( 1925)
emphasised points of agreement with both the Pteridosperms and with the Angiosperms. On
the whole, work since that date has made the Caytoniales seem even more isolated; the fruit in
particular is strictly Gymnospermous in pollination. The general organisation of the sporo
phylls seems Pteridosperm-like (though the fruit is still to be explained); the seeds are like
those of certain Bennettitales, and to a less extent the Angiosperms and the leaves, while
unusual in their form, have a distinctly Angiosperm-like epidermis (see Thomas 1925; Harris
1951).
Two organs tentatively referred to the Caytoniales are the isolated seed Amphorispermum
(included here) and the microsporophyll Pramelreuthia Krausel ( 1949). This, however, may be
nearer Harrisotheca Lundblad (1961) which belongs to a very different plant.
The evidence for attributing the various organs to one genus is the combination of the
evidence of association and the evidence of agreement in structure since no specimen showing
continuity has yet been discovered.
1. Evidence of Association
This is now overwhelming. It was at first untidy since the incompletely resolved suites of
organs of two species were mixed in the Gristhorpe Bed (Thomas 1925, 1931). However in
the Basal Liassic rocks of East Greenland a single species is involved and this is represented by
the same suite of organs in three localities (Harris 1932a, 1937). A Caytonia-like fruit is
associated with a Sagenopteris in the Swedish Rhaetic (Lundblad 1948). Then in Yorkshire the
two species of the Gristhorpe Bed have now been fully separated. One of these (leaf and fruit)
apparently occurs in Sardinia (Edwards 1929) and also in a second locality in Yorkshire. A
third Yorkshire species is now known though not yet fully distinguished and its leaf and
reproductive organs are associated in several localities. If the Caytoniales were among the
2
CA YTONIALES 3
commonest Yorkshire fossils such association would have little significance but they are by
no means common and fruits and anthers in particular are scarcely ever met without leaves.
At present Caytonialean leaves and reproductive organs are known associated in nine different
localities.
The occurrence of pollen grains of Caytonanthus inside the micropyles or nucellar beaks of
Caytonia seeds is intimate association. All suitable seeds of all four species show them and no
other kind of pollen has been recognised in this position. Even Caytonia seeds taken from a
coprolite showed this pollen.
2. Agreement in Structure
Thomas (1925) emphasised the resemblance between the cuticle of Sagenopteris petioles
and the rachises of both Caytonia and Caytonanthus from the Gristhorpe Bed, but as the
separate species were not fully discriminated the resemblance was generic rather than specific.
Now that the difference in the epidermal cells of the two Yorkshire species is realised, it is
possible to recognise the species of origin of each organ. In Sagenopteris colpodes of the
Gristhorpe Bed the cells have fine, sinuous walls on the lamina and jagged thickenings on the
petiole where sac-like trichomes are numerous. In S. phillipsi the cells have broad, straight
walls throughout and trichomes are rare. Just the same features are recognisable in the fruiting
rachises and probably in the microsporophyll rachises (though the evidence for Caytonanthus
oncodes is less perfect). Additional support is given by the Greenland species which has
glandular trichomes on fruit and leaf (Harris 1933).
Genus SAGENOPTERIS Presl, 1838: 164
EMENDED DIAGNOSIS. Leaf petiolate, petiole normally bearing two pairs of leaflets at its
apex, petiole and leaflets shed by absciss layers. Leaflet lanceolate with a main vein at a greater
or less distance distal to the mid-line; lateral veins arising at a small angle, but curving out
wards, forking and anastomosing to form obliquely elongated meshes, ultimate veins ending
freely at the margin.
Lamina cutinised; stomata confined to lower side, oval, guard cell surface flat but with a
sunken region around aperture, stoma surrounded by a perigenous ring of subsidiary cells.
TYPE SPECIES. Filicites nilssoniana Brongniart (1825 : 218).
DISCUSSION. The name applies to normal foliage leaves but is extended to cover small
leaves and minute scale leaves. For convenience also a twig is described here under the same
name but were the stem better known it would deserve a separate name.
Petiole. The following points have been noted. The petiole base is only slightly expanded
and shows a clean abscission surface. On the shoot (of S. phillipsi) there is a clearly marked
imprint of a single curved vascular strand on the leaf base scar. At the top of the petiole, the
scars of the four leaflets are in two clearly marked pairs and are on the upper surface (reaching
but not going below the petiole margin). There are two strong ridges (inS. colpodes) beginning
at the lower pair of leaflet scars and passing down the upper surface of the petiole, so as to
delimit a median groove. The back of the petiole is smooth, but inS. phillipsi it is ribbed. The
leaflets are abscissed from clean scars which show the imprint of a single median bundle.