Leliacladus Batista & L.Kunzmann, 2024

Genus Leliacladus Batista & L.Kunzmann nov.

Figs. 2–9 View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig .

Plant Fossil Registry Number: PFN003297.

Etymology: In honour of Lelia Duarte (1930–2013), a pioneering Brazilian paleontologist and paleobotanist, author of Brachyphyllum castilhoi redescribed in this work.

Type species: Brachyphyllum castilhoi Duarte, 1985 ≡ Leliacladus castilhoi ( Duarte, 1985) Batista & L.Kunzmann gen. nov. et comb. nov. (see below).

Diagnosis.—Foliated shoots, conspicuously thick, isotomous trifurcate and bifurcate branching mode. Leading branches cylindrical, frequently with cup-shaped apices, lateral branches claviform. Branches bear uniform Brachyphyllum - type adpressed leaves. Leaf epidermises smooth, with cyclocytic stomatal complexes abaxially, mostly arranged in loose and ill-defined rows. Xylem tracheid walls with abietinean radial pitting, one or two large pits per cross-field.

Leliacladus castilhoi ( Duarte, 1985) Batista & L.Kunzmann gen. nov. et comb. nov.

Plant Fossil Registry Number: PFN003298.

Basionym: Brachyphyllum castilhoi Duarte, 1985 : pl. 1: 1–3.

Epitype: MPPCN PL 6752 , selected herein, Figs. 2 View Fig , 4–7 View Fig View Fig View Fig View Fig .

Plant Fossil Registry Number: PFN003299

Type locality: Antônio Finelon Mine (S 07°07′22.5″ and W 39°42′01″), Nova Olinda municipality, Ceará, Brazil GoogleMaps .

Type horizon: C5 limestone unit, Crato Formation, Santana Group, Araripe Basin; lower Aptian, Lower Cretaceous ( Assine et al. 2014; Nascimento et al. 2023; Gobo et al. 2023).

Emended diagnosis.—Foliated sparsely branched shoots, conspicuously thick; leading branches cylindrical and straight, lateral branches claviform, arranged in two ranks; isotomous trifurcate and bifurcate branching modes. Main axes either terminate into slightly tapering rounded apices or into widened shallow cup-shaped apices. Branches completely and densely covered by uniform Brachyphyllum - type leaves, helical phyllotaxis. Nine and 10 contact parastichies clockwise and counterclockwise on the leading branches, and seven contact parastichies clockwise and counterclockwise on the claviform branches. Free apical leaf parts very small and adpressed, margin frilled. Leaf epidermises smooth, cyclocytic stomatal complexes on abaxial side, randomly arranged in apical and central parts, in loose and ill-defined rows at the base. Xylem tracheid walls with areolate pits, one or two large pits per cross-field. Uniseriate rays, one to three cells high.

Our emendation of the specific diagnosis encompasses characters that are not observable in the holotype. To demonstrate these diagnostic characters, MPPCN PL 6752 is proposed as the epitype ( Turland et al. 2018) .

Description.—In order to demonstrate that all the specimens from the two formations belong to a single fossil-species, the materials from the formations are described separately before being compared.

Crato Formation material: MPPCN PL 6752 and MMG PB SAK 59 represent portions of larger shoot systems and consist of differently shaped sterile foliated axes that exhibit sparse branching ( Figs. 2 View Fig , 3 View Fig ). These branches are composed of (i) main cylindrical long axes of two orders with conspicuous widths, and (ii) shorter lateral cup-shaped (claviform) branchlets with remarkable widths that do not branch out. All axes are three-dimensionally preserved, but markedly flattened. Thinner and slender (pen-)ultimate-order axes or their putative scars are not observed. In MPPCN PL 6752, one main axis shows isotomous trifurcate branching, while another shows isotomous bifurcate branching and a third branching axis is probably not preserved or hidden in the host sediment ( Fig. 2 View Fig ). MMG PB SAK 59 also exhibits seemingly trifurcate branching in one case, but this is less visible ( Fig. 3 View Fig ).

The main cylindrical axes terminate into two types of apices: a slightly tapering rounded apex and a widened, shallow cup-shaped (caliculatous) apex ( Fig. 2 View Fig ). The latter seems to be a supporting unit for larger organs, although these were not preserved. The claviform branchlets are borne in two ranks on the main axes (opposite phyllotaxis); the two remaining sides of the main axes show no scars of putatively removed or detached branchlets. The branchlets spread at acute angles and are often rather adpressed to the main axes. The claviform branchlets have their widest diameter approximately in the middlle or after two-thirds of their entire length, while they markedly taper towards their bases and apices. The latter are obtuse-rounded in shape.

MPPCN PL 6752 presents four larger leading axes, ranging 14–14.9 mm in width. The largest preserved cylindrical axis fragment is 215 mm long, but may have originally been longer, since the specimen is broken. The secondary (terminal) cylindrical branches are 85–109 mm in length and 11–12 mm in width, mostly 11.5 mm. Ten of the terminal branches carry a widened, shallow cup-shaped (caliculatous) apex. These structures show modified and condensed scale leaves. The cup-shaped structures are 16–21 mm wide markedly wider than their supporting axes. Among the claviform branchlets are obviously younger and ontogenetically older elements. Overall these measure 7–38 mm in length and 3–90 mm in width ( Fig. 2 View Fig ). In MMG PB SAK 59, which is a 490 mm long shoot portion, the cup-shaped apices of the main axes are not present. Instead, one of the main secondary cylindrical branches exhibits a slightly tapering obtuse-acute apex. The eight claviform branchlets are 17–50 mm in length and 9–16 mm in width.

All the branches are densely covered by scale leaves in a helical phyllotaxis. The dense arrangement does not vary between the older cylindrical and younger claviform axes ( Figs. 2A 2 –A View Fig 4 View Fig , 3A View Fig 2 View Fig , A 3 View Fig ). The leaves are exclusively of the Brachyphyllum - type, and do not transition to the Pagiophyllum type on the main axes, i.e., to leaves that are much longer than wide. The leaves are differently preserved; complete leaves are rare while abraded leaf cushions or even cushion marks are more commonly present. There are no leaf scars pointing to leaf abscission. In the secondary cylindrical branches with cup-shaped apices, there are nine and 10 contact parastichies arranged in a clockwise direction and the same numbers arranged in a counterclockwise direction. On the claviform branches, there are seven clockwise and seven counterclockwise contact parastichies ( Figs. 2A View Fig 4 View Fig , 3A View Fig 2 View Fig ). The leaves comprise a large cushion and a very small triangular free apical part; the entire abaxial surface is rhombic in outline. The leaf bases are acute and the apices are acute-obtuse, but both are almost symmetrical in shape ( Figs. 2A View Fig 4 View Fig , 3 A3 View Fig ). The apices only slightly overlap the neighboring leaves ( Fig. 3A 3 View Fig ). The free leaf parts are 0.2–0.3 mm long. The leaf blades are markedly thick (coriaceous), tapering to a thin margin consisting of a rim of elongated epidermal cells oriented almost at right angles to the margin. The rim is ~ 0.05 mm wide. The cushions and cushion marks present on the main branches measure 2.5–3.0 mm in width and 2.5– 3.1 mm in length. However, they are mostly 2.6 mm wide and 2.6 mm long. On the slightly tapering obtuse-acute apices of the main axes, the sizes of the leaves gradually decrease. The leaves of the cup-shaped apices are larger than the leaves of the branches, measuring, on average, 3.1 mm in width and up to 3.4 mm in length ( Fig. 2A View Fig 3 View Fig ).

Leaf epidermis: The epidermal cell layer was preserved three-dimentionally and the cell luminae are filled with iron oxide. The cuticles are absent, and thus there is no potential microrelief of the outer cuticle surfaces visible. It was only possible to study the abaxial leaf surface; the remains of the adaxial surface could not be obtained.

The abaxial surface is characterized by a special distribution pattern of stomatal complexes. In the lower and central parts of the leaf, the stomata are arranged in loose longitudinal rows. In the central and apical leaf parts, the rows become ill-defined and the stomata are distributed more randomly and in a scattered fashion. No stoma directly adjoins another. There are always several ordinary epidermal cells between neighboring stomata of the same row and between the stomata of adjacent rows, as well as between the more scattered stomata in the apical parts. The stomatal complexes of the lower and central parts are longitudinally oriented, whereas the stomatal complexes of the apical part are more perpendicularly oriented in relation to the long leaf axis. The stomatal complex is generally cyclocytic with a ring of 5–6 subsidiary cells that seem to be very slightly sunken in a few cases ( Fig. 3A View Fig 5 View Fig , A 6 View Fig ). The subsidiary cells are isodiametric to short rectagnular (less than twice as long as wide) in shape, with straight anticlinal walls. The two guard cells are only faintly visible, but they are sunken. The ordinary epidermal cells are arranged in relatively well-defined longitudinal rows in the lower and central parts of the leaf, and more irregularly arranged in the apical part. In the former parts, the epidermal cells are elongated and subrectangular in shape, while in the latter part, they are shorter and often isodiametric in shape (4- to 6-sided). All the anticlinal walls are straight. Towards the leaf margin, the ordinary epidermal cells became more elongated again and are often very slightly curved in their longitudinal axes, diverging towards a rectangular orientation to the leaf margin. This arrangement of columnar marginal cells at a scarious leaf margin is known as “marginal frill” ( Fig. 3A View Fig 4 View Fig ). No trichomes, papillae or glands are observed on the visible leaf surfaces.

Stem: The xylem is homoxylic composed of tracheids with little to no intercellular spaces. In cross-section, the tracheids are rounded, square or pentagonal in shape, and arranged radially, without growth-rings. However, there are marks that look like growth rings. These are actually artifacts caused by cutting the sample with a knife to prepare to the SEM ( Fig. 4A View Fig 1 View Fig , A 2 View Fig ). The lumens are about 7.8 µm in diameter and the walls are about 5.3 µm thick. In longitudinal view, the tracheids are narrow and long, organized in an intrusive way, and exceed 900 µm in length ( Fig. 4A View Fig 3 View Fig ). The radial tracheid walls show well-separated uniseriate areolated pits (abietinean radial pitting). The pit opening diameter dimensions is ~2 µm ( Fig. 4A 4 –A View Fig 6 View Fig ). In some tracheids, the pits appear simple, but this may have resulted from taphonomic processes ( Fig. 4A View Fig 7 View Fig ).

Uniseriate rays are visible in radial and tangential sections ( Figs. 4A View Fig 3 View Fig , 5 View Fig , 6A View Fig 1 –A View Fig 3 View Fig ). These vary from one to three cells in height, with two cells being the most frequent. The rays are ~6 µm in width and 15–18 µm in height. Rays with thicker walls are visible ( Fig. 6A View Fig 3 View Fig ). The cross-field pitting is similar to the podocarpoid type, where usually only one pit in the cross-field. In our material, there are usually one or two simple and large pits per cross-field, measuring 3.7 µm in average diameter ( Figs. 5A View Fig 1 View Fig , A 3 View Fig , A 4 View Fig ). In one case, a branch attachment scar can be seen. The scar is ~227 µm high and 119 µm wide ( Fig. 6A View Fig 4 View Fig ). The tracheids in this area have a lumen diameter of ~4 µm and walls ~3 µm thick.

Shallow cup­shaped structures: The anatomical details of these structures show little vascularization and the presence of a large number of parenchyma cells ( Fig. 7A View Fig 1 –A View Fig 4 View Fig ). In the vascular strands, the xylem is well organized ( Fig. 7A View Fig 5 View Fig ). In longitudinal view, the tracheids show scalariform thickenings in the inner part of an isolated cell next to the parenchyma cells ( Fig 7A View Fig 6 View Fig ). The parenchyma cells are irregular in shape, ranging from rounded to rectangular. The more rounded ones have diameters of 20–50 µm, while the rectangular ones average 75 µm in length and are 20–35 µm wide.

Romualdo Formation material: DBAV-UERJ93Pb (holotype), MCNHBJ 171, and MCNHBJ 176 represent portions of larger branches that exclusively consist of differently shaped foliated axes ( Fig. 8 View Fig ). These fragments are composed of two orders of branching. The branches are remarkably wide and three-dimensionally preserved, although somewhat flattened. Thinner and slender ultimate or penultimate order axes, or their putative scars, are not visible in the MCNHBJ specimens, although the diagnostic ultimate-order claviform axes are present in the holotype DBAV-UERJ 93 Pb ( Fig. 8A View Fig 1 View Fig ).

DBAV-UERJ 93 Pb is a simple, non-furcating portion of a cylindrical main branch that is 190 mm long and 20 mm wide ( Fig. 8A View Fig 1 View Fig ). Seven distichously arranged pairs of claviform lateral branchlets are preserved and attached at acute angles to the main axis. The remaining surface of the main axis shows no scars from additional, putatively detached claviform branchlets.

MCNHBJ 171 shows trifurcated branching, although the lateral branches are not preserved, with only the bases at the main branch being present ( Fig. 8B View Fig ). From the main branch, another branch emerges above the trifurcation node. The main axis fragment is 169 mm long, but may have been longer in life, since the specimen is broken. It is 180 mm wide at the widest point and 130 mm wide at the branch base. This specimen is partially flattened, especially in the outermost area, where the leaves are preserved. The secondary and ultimate claviform branch is 100 mm long, 10 mm wide at the widest point and 8 mm wide at the base.

MCNHBJ 176 shows trifurcated branching, with two larger branches visible and a third branch being partially covered by sediment, but with its base exposed ( Fig. 8C View Fig ). There is a fourth branch, but its base is not preserved. Of the three branches that emerge from the same point, only one is fully exposed, and this is 145 mm long, 13 mm wide at its widest point, and 9 mm wide at its base. The other two branches are embedded in the sediment, so it is not possible to measure their lengths. Their widths at the base are 7 mm.

All branches of the three specimens are densely covered by scale leaves in a helical phyllotaxis. In DBAV-UERJ 93 Pb~10 contact parastichies, arranged in clockwise and anticlockwise directions, are visible. In MCNHBJ 171 and MCNHBJ 176, only the leaf parastichies of the main branches can be counted. These are arranged in 7–9 contact parastichies in clockwise and anticlockwise directions.

The dense arrangement of scale leaves does not vary between axes. The leaves are almost exclusively of the Brachyphyllum - type, although some leaves of the Pagiophyllum type occur on the main axes. The leaves are rhombic in abaxial outline, consisting of a large cushion and a tiny free apical part adpressed to the axis ( Fig. 8A View Fig 2 View Fig , A 3 View Fig ). The bases are acute and the apices acute-obtuse, but both are almost symmetrical in shape. They have relatively smooth, although somehow shriveled, surfaces, a few cases showing a narrow longitudinal keel on the abaxial side ( Fig. 8A View Fig 3 View Fig ). The free triangular apical leaf part only slightly overlaps or does not overlap the neighboring leaf. The leaves are generally isodimensional in length and width (up to 3 mm), although a few leaves are slightly longer than they are wide, being 4 by 3 mm, without a marked change in their shapes compared to the majority of the isodimensional leaves. The leaves that are longer than the width of the cushion fit the diagnostic characters of the Pagiophyllum type leaf. The free leaf parts are 1.5–2 mm long. The leaf blades are markedly thick (coriaceous).

Leaf epidermis: Only DBAV-UERJ 93 Pb and MCNHBJ 176 show preserved epidermal features. Due to the preservation mode of the fossils, the epidermal cell layer is also three-dimentionally preserved and the cell luminae are filled with calcite. The cuticles are not preserved and so any potential microrelief on the outer cuticle surfaces is not visible. Only the abaxial leaf surface was visible, while the adaxial surface was not obtained.

The epidermal cell structure of the leaves could be only studied by SEM. The differently shaped ordinary epidermal cells are rectangular, rounded or oval in outline ( Fig. 9A View Fig 1 – A View Fig 3 View Fig , B). They are ~10.6 µm wide and 22 µm long when rectangular, and arranged in longitudinally oriented rows at the leaf bases. The stomatal complexes are randomly oriented from the central part of the leaf to the apex, and distributed in ill-defined rows at the base of the leaf ( Fig. 9A View Fig 1 –A View Fig 3 View Fig , B). The complexes do not share any subsidiary cells and are always separated from each other by at least two ordinary epidermal cells. The cyclocytic stomatal apparatuses measure between 33 and 40 µm in width and between 57 and 72 µm in length. Five or six subsidiary cells surround the slightly sunken guard cells. The stomatal apertures at the bases of the leaves are oriented longitudinally, although in rare cases, they can also be more or less obliquely oriented, as is mainly the case from the central part to the apex. The subsidiary cells are isodiametric at the poles and short rectangular (less than twice as long as wide) in shape on the lateral sides of the complexes and they show straight anticline walls. No trichomes, papillae or glands are visible.

Stem: It was only possible to observe the anatomical characteristics of the stem in MCNHBJ 176 and MCNHBJ 171. Both specimens have poorly preserved xylem structures, which only show the general shape of the tracheids ( Fig. 9B View Fig 2 View Fig , C). No other features could be observed.

Stratigraphic and geographic range.—Aptian, Lower Cretaceous; Crato and Romualdo formations, Santana Group, Araripe Basin; NE Brazil ( Assine et al. 2014; Nascimento et al. 2023; Gobo et al. 2023).