THE RED HOT LEAF FLORA
Specimen. USNM 535047 (Figure 2.1, 2.2; site 1). Morphotype RH06.
Distinguishing features and description. Width mostly uniform.
Numerous, closely spaced secondary veins strongly decurrent on primary vein,
diverging at low angles and dichotomizing multiple times. A lobe fragment with
preserved length 3.8 cm, preserved width 1.6 cm.
Comments. The specimen clearly matches the distinctive venation of
Lygodium (Manchester and Zavada, 1987). Lygodium leaves are typically
digitate-lobed, and this specimen is most likely a fragment of a single lobe.
1930) reported several Lygodium species from
various localities of the Gulf Coast Eocene, including L. kaulfussi which
was widespread in the Eocene of North America, Europe, and Asia (Manchester and Zavada 1987).
Manchester and Zavada (1987) concluded that all of Berry's species
are indistinguishable from
L. kaulfussi, which they considered the sole recognizable species of
Lygodium in the Northern Hemisphere Eocene. The Lygodium considered
here is also not distinguishable from L. kaulfussi and is accordingly
placed in that species.
reported two schizaeaceous spore types from the Red Hot Truck Stop locality that
could have been produced by Lygodium.
Specimen. USNM 535048 (Figure 2.3; site 2). Morphotype RH12.
Distinguishing features. Entire margin, acute basal pair of secondaries,
and opposite percurrent tertiary veins that are approximately perpendicular to
the primary vein.
Description. Lamina elliptic, symmetrical, preserved length 8.3 cm,
preserved width 4 cm; estimated l:w ratio 2.25:1; base convex, base angle acute,
apex straight, apex angle acute; margin entire. Venation pinnate, primary vein
straight. Secondary veins eucamptodromous, straight to slightly curved, angle
from midvein 28°–65°, basal pair strongly acute, spacing irregular. Tertiary
veins opposite percurrent, approximately perpendicular to the primary vein, or
random reticulate. Fourth order veins random reticulate (photograph poorly).
Comments. The combination of entire margin, acute basal secondaries, and
tertiary veins oriented perpendicular to the midvein is widely prevalent among
Lauraceae, to which we tentatively assign this single, poorly preserved fossil.
Specimens. USNM 535050 (Figure 3.1; site 2). Morphotype RH03.
Distinguishing features and description. Two orders of parallel venation
(A and B veins) with straight, curved, or sigmoidal oblique cross
veins intersecting the parallel veins, both A and B. There are
approximately 2–3 B veins between each pair of A veins. The cross
veins run obliquely to the A and B veins and can be straight,
curved, or sigmoidal.
Comments. The parallel venation pattern and sigmoidal, oblique cross
veins are characteristic of several monocot groups. Due to the lack of
preservation details in these fragmented compression fossils, lower order
taxonomic assignments cannot be made.
Specimens. USNM 535051 (Figure 3.2, 3.3; site 1). Additional deposited
specimens: four from site 1 and one from site 2. Morphotype RH02.
Distinguishing features. Numerous thin, decurrent secondaries and
intersecondaries that join a prominent intramarginal vein, and an entire margin.
This distinctive architecture can be found in many genera of Myrtaceae (Carr et
Description. Lamina oblong, symmetrical, narrow; preserved l:w ratio (l:w)
~5:1; precise l:w unknown; preserved length 4.7–7.0 cm, estimated to 8 cm; width
1.3–2.0 cm; base angle acute, apex not preserved; margin entire, fimbrial vein
present. Venation pinnate; primary vein straight, thick basally. Secondary veins
numerous (6–9 per cm), irregularly spaced, arising decurrently from primary vein
at consistent 65° angles curving near intramarginal vein. Intersecondary veins
strong, ~1 intersecondary per secondary with most intersecondaries reaching the
intramarginal vein. Tertiaries not visible.
Comments. Berry (e.g., Berry 1930) assigned various Eocene Gulf Coast
leaves to myrtaceous genera such as Calyptranthes Swartz (1788),
Eugenia Linnaeus (1753), and Myrcia de Candolle (1827),
although these assignments are doubtful at the generic level (Manchester et al.
1998) and have never been revised. More recently, Dilcher and Lott (2005)
tentatively assigned myrtaceous leaves from the middle Eocene Powers Clay Pit to
Specimens. USNM 535052 (Figure 4; site 1). Additional deposited
specimens: 24 from site 1. Morphotype RH07.
Distinguishing features. Conspicuously pulvinulate, marginally inserted
petiolule; entire margin. Secondary veins diverge at low angle, extend distally
Description. Lamina ovate to elliptical, symmetrical, usually narrow
(preserved l:w 2:1 to 4:1; estimated l:w ~3:1; preserved length 1.0–4.5 cm,
estimated 1.4–6 cm; width 0.7 cm to estimated 2.0 cm), base convex, base angle
acute; apex generally straight, apex angle acute; margin entire, fimbrial vein
present. Petiolule pulvinulate. Venation pinnate, primary vein straight.
Secondary veins weak brochidodromous to eucamptodromous, extending distally,
straight to slightly curved; ~3-4 secondaries/cm, arising from the midvein ~25°,
spacing irregular, vein angles gradually decreasing and becoming more uniformly
spaced proximally. Secondary veins closely spaced near the margin, becoming
nearly parallel with margin, then joining superjacent secondary or diminishing.
Intersecondaries weak to strong, not consistently present between each pair of
secondaries. Tertiary veins opposite percurrent, perpendicular to the midvein
between the closely spaced secondary veins near margin. Fourth order veins
random reticulate; fifth order veins random reticulate to regular polygonal
reticulate; freely ending veinlets (FEVs) unbranched.
Comments. Legumes have been recognized in the Gulf Coast floras since
Berry's time, and middle Eocene representatives have been extensively revised
and Dilcher, 1990a,
1992). This morphotype is similar to Ormosia sp. reported by
reported two pollen types from the Red Hot Truck Stop locality assignable to
Fabaceae or Sapotaceae
Specimen. USNM 535053 (Figure 5; site 2). Morphotype RH13.
Distinguishing features. Base acute; margin irregularly serrate, tooth
apices rounded, tooth apices weakly glandular. Secondary divergence angle ~65°;
secondaries curve steeply distally near margin; intersecondaries weakly
developed. Tertiary veins percurrent, sinuous, junctions with subjacent
secondaries perpendicular to obtuse.
Description. Lamina elliptic to ovate, symmetrical, narrow (preserved and
estimated l:w ~3:1; preserved length 9.3 cm, estimated 12 cm; preserved width
3.6 cm, estimated 4 cm). Base angle acute, base shape unknown; apex angle and
shape unknown; margin serrate, fimbrial vein present. Venation pinnate, primary
vein straight. Secondary veins craspedodromous, straight near midvein, then
steeply curving near the margin, 10–12 pairs, angle 60–75°, spacing irregular,
angles smoothly decreasing proximally. Intersecondary veins weak; agrophic veins
absent. Tertiary veins opposite percurrent, straight to sinuous; angle to
primary obtuse, decreasing exmedially, junctions with subjacent secondaries
perpendicular to obtuse. Fourth order veins random reticulate. Teeth small and
in one order, weakly glandular, sinuses rounded, spacing irregular, about three
teeth per centimeter.
Comments. The venation of the single specimen is preserved only as
faint impressions in the matrix and photographs poorly (Figure 5); nevertheless,
it is surprisingly complete. In particular, the opposite percurrent, straight to
sinuous tertiaries and their perpendicular to obtuse junctions with subjacent
secondaries are clearly but faintly visible (Figure 5.2, 5.3). Despite the
preservation, this fossil demonstrates the defining characteristics of
Platycarya foliage (Wing and Hickey 1984; extant Platycarya may have
simple or compound leaves depending on species). Pollen of this genus is also
found in the same sediments (Frederiksen 1998;
Harrington, 2003a). The specimen
corresponds best to the Eocene Western Interior taxa P. americana (Hickey
1977) and P. castaneopsis (Lesquereux)
Wing and Hickey (1984), whose
leaves have many differences with living Platycarya but whose fruits and
seeds are generically diagnostic (Wing and Hickey 1984). Due to preservation,
one character found in Platycarya leaves, the ascending vein from sinus
to superjacent tooth (Wing and Hickey 1984), was not observed.
Description. This morphogenus is erected for leaves having certain
characteristics found in the extant genus Rhabdophyllum
(1902a). The diagnostic characters of Rhabdophyllites, in combination,
are: a toothed margin; closely spaced, thin, and numerous secondary veins of the
"Clusia" type discussed by
Gentry (1993) and
Keller (2004); and distinct intersecondary veins.
Discussion. This morphogenus is assigned to Ochnaceae, which is the sole
extant family having the distinctive combination of toothed margin and "Clusia"
venation. The morphogenus designation and –ites suffix (Greek,
"having the nature of":
Brown 1956) conservatively allow placement in the family and highlight the
general similarity to extant Rhabdophyllum (tropical Africa) without
categorization to any extant genus.
Type species. Rhabdophyllites diapyros
Rhabdophyllites diapyros sp. nov.
Type material and illustration. Holotype: USNM 535054 (Figure 6), USNM
loc. 43409 (= site 1). Paratypes: USNM 535055 (Figure 7.1–3), USNM loc. 43409 (=
site 1) and USNM 535056 (Figure 7.4, 7.5), USNM loc. 41312 (= site 2). [Morphotype
Etymology. Greek, "red-hot, fiery" (Brown 1956). Named in memory of the
Red Hot Truck Stop, a popular local landmark, 1955–2000.
Distinguishing features. Elliptic leaf with single primary vein.
Secondary veins numerous, thin, closely spaced (3-8 mm apart along primary),
eucamptodromous; intersecondary veins well developed, closely spaced (2-3 mm
apart along primary), but both secondaries and intersecondaries vary and
intergrade in distance covered from midvein to margin before branching or
deflection; thus, individual intersecondaries are difficult to distinguish from
secondaries as well as tertiaries. Tertiary veins random reticulate; teeth
cryptic to conspicuous, best developed towards the apex.
Description. Lamina elliptic, symmetrical. Estimated length 10.5–14.5 cm,
width 4.5 cm; preserved l:w ratio 2.5:1; estimated l:w ratio ~3:1. Base convex,
base angle acute; apex angle acute, apex shape unknown; margin crenate to
serrate. Petiole not preserved. Venation pinnate; primary vein straight, thick,
apparently well lignified. Secondary veins eucamptodromous, straight to slightly curved, curving
distally approaching margin, 3-8 mm apart along primary, angle 50–65°, spacing
irregular, course infrequently deflected at tertiary vein junctions. Intersecondary veins well developed, 2–3 mm
apart along primary, one or more intersecondary per secondary, but highly
variable in strength and thus difficult to distinguish from secondaries and
tertiaries. Tertiary and fourth order veins random reticulate. Teeth small,
blunt, best developed towards leaf apex, possibly glandular but not diagnostic
due to preservation; looped accessory veins present in larger teeth (Figure
Comments. The distinctive, closely spaced, parallel, thin secondaries and
intersecondaries mark the "Clusia" venation type (Gentry 1993;
2004) found within many Clusiaceae
Lindley (1836b) and certain genera of Sapotaceae, such as Manilkara
Adanson (1763), Micropholis (Grisebach)
Pierre (1891), and many others; Vochysiaceae
Saint-Hilaire (1820), including
Qualea Aublet (1775) and Ruizterania
Marcano-Berti (1969); and Ochnaceae
de Candolle (1811a) such as Blastemanthus
Elvasia de Candolle (1811b), Euthemis
Jack (1820), Philacra
Dwyer (1944), Rhabdophyllum
van Tieghem (1902a), Schuurmansiella
Hallier (1913), and Tyleria
Gleason (1931). All four groups are
characteristically tropical in distribution (e.g.,
Heywood 1993). Leaves in Ochnaceae are often toothed, whereas the three other families listed uniformly
have untoothed leaves (Gentry 1993). An extremely rare exception is the Sapotaceae species Chrysophyllum imperiale (Linden)
Bentham and Hooker
(1876), which has vein architecture completely unlike this fossil. Thus, the
combination of "Clusia" venation and a toothed margin diagnoses the
fossils to Ochnaceae, the only other possibility being an extinct toothed genus
from one of the families mentioned above.
Of the extant genera we observed, those most similar to the fossil are
Philacra, Rhabdophyllum, and Schuurmansiella, which all have
toothed margins and distinct intersecondaries. Of these, Rhabdophyllum
has the least regular teeth and the most visibly distinct intersecondaries,
additional attributes of the fossil species. Good comparative examples are R.
arnoldianum van Tieghem (1902a) (Figure 8.1), R. penicillatum
van Tieghem (1902a) (Figure 8.2, 8.3), R. affine van Tieghem (1902a), R.
refractum van Tieghem (1902a), and R. welwitschi
van Tieghem (1902b)
(Figure 8.4, 8.5). However, the fossil species differs from Rhabdophyllum
in having intersecondaries of more variable and generally lower strength (weaker
course), as well as secondary veins that turn distally more strongly inside the
margin. We also note the Eocene Gulf Coast species Clusiaphyllum eocenicum
(Berry 1930, type specimen USNM 316794), whose venation does not resemble R.
diapyros in that its secondaries are strongly upturned near the margin and
join either a fimbrial vein or a strong ascending secondary vein; this single
specimen is fragmentary and is not toothed along the preserved margin.
The fossil record of other Malpighiales groups, as well as molecular clock
divergence estimates, suggests a Cretaceous origin for all Malpighiales families
(Davis et al. 2005). Fossil fruits that resemble the extant genus Ochna
Linnaeus (1753) have recently been found in the Late Paleocene of North
Dakota and are currently being described (Pigg and DeVore 2005). However, to our
knowledge, the distinctive specimens reported here are the most reliable fossil
leaves of Ochnaceae, a family with approximately 30 extant genera and 500
species, of mostly trees and shrubs, having tropical South America as its major
center of diversity within a pantropical distribution (Heywood 1993). Berry
described middle Eocene leaves from Tennessee (Berry 1930) and Río Negro,
Argentina (Berry 1938; dated in
Wilf et al. 2005) as species of Ouratea
Aublet (1775), but neither bears close resemblance to the extant genus. Although
there are scattered reports of fossil Ochnaceae pollen in the literature (Gruas-Cavagnetto
1976; Barbin 1992), these must be considered unreliable, until more detailed
analyses are done, because the extant pollen morphology is unspecialized and
thus very difficult to distinguish from similar groups (e.g.,
There appear to be no reliable pollen records of Ochnaceae older than Holocene
(e.g., Muller 1981).
Specimen. USNM 535057 (Figure 9.1, 9.2; site 1). Morphotype RH09.
Distinguishing features. Large, compound, irregular teeth;
craspedodromous, nearly cladodromous secondary veins branch conspicuously and
terminate into both tooth orders and into sinuses; thin but prominent
intersecondary veins; secondaries and intersecondaries irregularly angled.
Comments. Conspicuously forking to cladodromous secondary veins,
irregularly angled secondaries and intersecondaries, large and irregular to
compound teeth, and termination of secondary veins or branches thereof in
pointed tooth apices and sinuses comprise the characteristic architecture for
toothed Rhus leaflets (e.g.,
Wolfe and Wehr 1987;
Cevallos-Ferriz 2005). A few other genera in Anacardiaceae show some components
of this venation syndrome, including Loxopterygium
Bentham and Hooker
(1862) and Schmaltzia
Desvaux ex Small (1841), but it is best expressed
and most widely prevalent in Rhus.
possible Anacardiaceae pollen from the Red Hot Truck Stop section.
Lamina narrow (size data not available due to fragmentation), shape and angles
of apex and base unknown; margin serrate, fimbrial vein present. Venation
pinnate, primary vein straight. Secondary veins craspedodromous to cladodromous,
6–8 pairs preserved, thickness and angle irregular. Intersecondaries thin,
~parallel to secondaries, angle irregular. Tertiary veins random reticulate.
Teeth in two orders, ~four teeth/cm; teeth large, glandular; sinuses angular;
tooth apices pointed; secondary vein branches terminate in sinuses and compose
Incertae sedis, morphotype RH15
Specimens. USNM 535064 (Figure 9.3; site 1).
Distinguishing features. Strongly asymmetrical base; irregularly spaced
secondary veins that diverge off primary vein with a different divergence angle
on either side of the primary vein.
Description. Lamina (probable leaflet fragment), oblong, wide (preserved
l:w ratio 1.6:1, estimated l:w ratio ~2:1), base asymmetrical, decurrent, angle
acute, petiole attachment marginal. Margin entire, fimbrial vein present.
Venation pinnate; primary vein thick, curved basally; basal veins three.
Secondary veins craspedodromous, 8–10 pairs spaced irregularly, arising from
midvein decurrently at ~55°, curving distally near margin. Intersecondaries
weak. Tertiary veins random reticulate; fourth order veins regular polygonal
reticulate; fifth order veins random reticulate, FEVs unbranched where
Incertae sedis, morphotype RH16
Specimen. USNM 535065 (Figure 9.4; site 1).
Distinguishing features. Thick primary vein with strongly decurrent
secondary veins and prominent intersecondaries.
Description. Leaf fragment, base and apex characteristics unknown,
preserved lamina width ~2.5 cm; observed margin entire. Venation pinnate,
primary vein stout, tapering distally; secondary veins eucamptodromous or
craspedodromous, curved, thin, numerous (4 pairs in small exposed area),
decurrent on midvein with divergence 45–60°. Intersecondaries present,
conspicuous. Tertiary veins random reticulate; higher order venation not
Incertae sedis, morphotype RH04
Specimen. USNM 535058 (Figure 10.1, 10.2; site 1).
Distinguishing features. Two primary veins (probably three or more
originally) diverging from each other and connected by interior secondary veins.
Leaf possibly palmately lobed. High order venation and areolation unusually
well-preserved (Figure 9.2) for this flora, suggesting well-lignified veins.
Description. Fragment; lamina size, base, apex, and margin features
unknown. Primary venation apparently actinodromous or palinactinodromous;
preserved secondary venation interior, spacing decreasing basally, perpendicular
to primaries. Tertiary veins random reticulate, spacing close (1.5–3 mm). Fourth
and fifth order veins random reticulate; areolation moderately developed, five
or more sided; FEVs unbranched or one-branched.
Incertae sedis, morphotype RH05
Specimen. USNM 535059 (Figure 10.3, 10.4; site 1).
Distinguishing features. Rounded sinus (Figure 9.3, arrow), which
indicates this is a lobed leaf, and thick tertiary veins arising perpendicular
to the primary vein that join the subjacent secondary vein. The marked
difference in secondary vein divergence angle on either side of the lobe primary
(Figure 9.4) indicates that this is a left lateral lobe. From same locality as
RH04 but lacking the distinctive impressed areolation (Figure 9.2).
Description. Preserved lobe narrow, lobe sinus rounded; margin entire,
fimbrial vein present. Venation presumably actinodromous or palinactinodromous.
Secondary veins eucamptodromous. Tertiaries arising from midvein thick,
divergence from primary perpendicular, then deflecting to subjacent secondary;
tertiary veins arising from secondary veins. Higher-order venation present but
Incertae sedis, morphotype RH08
Specimens. USNM 535060 (Figure 11.1; site 1). Additional deposited
specimens: five from site 1.
Distinguishing features. Ovate blade, entire margin, and eucamptodromous
or weak brochidodromous, irregularly spaced secondary veins, diverging from the
midvein at ~40°, and then curving towards the margin with few, weak
Description. Lamina elliptic to ovate, symmetrical, narrow (preserved and
estimated l:w ratio ~3:1; preserved length 1.2–6.5 cm, estimated 3.5–7 cm;
preserved width 1.0–3.0 cm, estimated 1.3–3.2 cm); margin entire, fimbrial vein
present. Venation pinnate; primary vein straight. Secondary veins
eucamptodromous to weakly brochidodromous, ~2–3 secondaries per cm, divergence
angle ~40°, gently to sharply curving off primary vein and curving apically near
margin; spacing irregular. Intersecondary veins few to absent. Tertiary veins
random reticulate, oriented nearly perpendicular to primary vein near margin
where secondaries are closely spaced; fourth order veins random reticulate.
Incertae sedis, morphotype RH14
Specimen. USNM 535063 (Figure 11.2, 11.3; site 2). Additional deposited
specimens: five from site 2.
Distinguishing features: Poorly preserved morphotype with eucamptodromous
or weakly brochidodromous secondary veins, which diverge from the midvein at
45°. Although very generalized in appearance, RH14 is distinct from other
morphotypes presented here in the combination of eucamptodromous or weakly
brochidodromous secondary venation, entire margin, and a high length:width
Description. Lamina elliptic, probably symmetrical prior to preservation,
narrow (preserved l:w ratio ~5:1, estimated l:w ratio ~3.5:1; preserved length
5.7–10 cm; preserved width 2.5–4.5 cm); base angle acute, apex rounded, apex
angle obtuse; margin entire, fimbrial vein present. Venation pinnate; primary
vein straight, width decreases distally. Secondary veins eucamptodromous or
weakly brochidodromous, straight-slightly curved, divergence angle ~45°. Higher
order venation not preserved.
Incertae sedis, morphotype RH10
Specimens. USNM 535061 (Figure 12.1, site 2). Additional deposited
specimen: one from site 2.
Distinguishing features. Acute base and apex angles, and secondary veins
diverging off the midvein at ~65°.
Description. Lamina elliptic, narrow (preserved l:w ratio ~3.3:1,
estimated l:w ratio ~3.5:1; preserved length 12.5–13.5 cm; width 3.5 cm); base
apparently asymmetrical, base angle acute; apex straight and acute; margin
entire, fimbrial vein present. Venation pinnate; primary vein width decreasing
distally. Secondary veins eucamptodromous to weakly brochidodromous, slightly
curved, divergence angle 65°; agrophic veins absent; intersecondary veins weak
if present. Tertiary veins random reticulate.
Incertae sedis, morphotype RH11
Specimen. USNM 535062 (Figure 12.2, 12.3; site 2).
Distinguishing features. Large, blunt, widely spaced, semitriangular
teeth, concave on both flanks; craspedodromous secondary veins lose gauge as
they enter teeth.
Description. Lamina apparently elliptic; margin serrate, fimbrial vein
absent. Preserved length 5.6 cm (estimated 9 cm); preserved width 2.8 cm
(estimated 3 cm). Venation pinnate; secondary veins craspedodromous, spacing
irregular, angles uniform. Intersecondary veins absent. Tertiary veins opposite
percurrent. Teeth of one order, spacing ~1 tooth/cm, large, concave on both
flanks, sinuses angular, apices glandular; secondaries lose gauge, or decrease
in width, entering teeth.
Incertae sedis, morphotype RH18
Specimen. USNM 535067 (Figure 12.4; site 1).
Distinguishing features. Basally eucamptodromous and apically
brochidodromous secondary veins that turn upwards sharply along the margin
towards the apex of the leaf, and well-developed opposite percurrent tertiary
veins that change course with the secondary veins.
Description. Lamina elliptic, symmetrical; narrow (preserved l:w ratio
2.4:1; estimated l:w ratio ~2.1:1; preserved length 6 cm, estimated 7 cm;
preserved width 2.2, estimated 3 cm), base and apex angle acute but shape
indeterminate; margin entire. Venation pinnate, primary vein slightly sinuous.
Secondary veins brochidodromous apically, eucamptodromous basally, extend
straight towards the margin, turning steeply near margin, 9 pairs, divergence
angle ~50°, spacing regular. Tertiary veins opposite percurrent; angle to
midvein obtuse admedially, perpendicular to midvein near margin. Higher order
venation present but poorly preserved.
Incertae sedis, morphotype RH17
Specimen. USNM 535066 (Figure 12.5, 12.6; site 2).
Distinguishing features. Entire margin, acute base. Weakly
brochidodromous, thin secondary veins diverging from the midvein at ~55°; random
reticulate tertiary veins.
Description. Lamina apparently elliptic, narrow (preserved l:w ratio
2.5:1, estimated l:w ratio 2.25:1; preserved length 2.5 cm, estimated 4.5 cm;
preserved width 1.5, estimated 2 cm); base cuneate, base angle acute; margin
entire, fimbrial vein present; petiole attachment marginal. Venation pinnate;
secondary veins weakly brochidodromous, looping close to margin, 5 pairs
observed, divergence angle ~55°, spacing increasing basally. Intersecondary
veins well developed; tertiary veins random reticulate.
Incertae sedis, cuticle morphotype 1
Specimen. USNM 535049 (Figure 13; site 2). Numerous additional specimens
present in matrix but not inventoried.
Distinguishing features. The strap-shaped cuticle fragments are often
preserved yellow to orange. Cells are visible under stereoscope (Figure 13.1),
with both epidermis and hypodermis preserved. The epidermal surface is striated,
and stomata are present.
Description. Strap-shaped cuticle, ~ 5.5 mm width. Epidermal cells
elongate (width 14-26 m), with surface striations, cells more elongate along
leaf margin. Hypodermis thick-walled, cells less elongate than those of
epidermis. Stomatal areas sunken in relation to surrounding epidermis, guard
cell pairs (24-28 m in polar length) oriented obliquely to long axis of
surrounding epidermal cells; subsidiary cell arrangement paracytic. Venation
Comments. Paracytic stomata and strap-shaped leaves are suggestive of
Monocots. This cuticle morphotype may have been produced by the same source
species as monocot compression morphotype RH03 described above, but without
preserved venation, this is impossible to establish.
Incertae sedis, cuticle morphotype 2
Specimen. USNM 535888 (Figure 14; site 2). Numerous additional specimens
present in matrix but not inventoried.
Distinguishing features. The cuticle is preserved in fragments of
variable shape that are dark brown. Cells are difficult to distinguish under
stereoscope, and only epidermis is preserved. The epidermis lacks surface
striations and bears densely distributed pore-like structures with raised rims.
Description. Cuticle fragments, epidermal cells elongate, surface
striations lacking, surface rough to smooth under ESEM. Hypodermis and stomata
not present. Epidermis bears densely distributed pore-like structures with
raised rims, pores filled with debris (visible under ESEM).
Comments. The pores consistently lack remnants of guard cells or trichome
bases. Thus, the pores appear to be a true feature of the cuticle, rather than
sites of detached or degraded stomatal areas. Open pores of varying morphology
are produced by thalloid liverworts (Ligrone et al. 2007).