Fern-like Plants Establishing the Understory of the Late Devonian Xinhang Lycopsid Forest

Forests appeared during the Middle to Late Devonian, but Devonian forests and their compositions are still rarely known. Xinhang forest was reported as the largest Devonian forest, with lycopsid trees of Guangdedendron micrum Wang et al. A fern-like plant Xinhangia spina Yang and Wang with shoots and anatomy, was previously described from this forest, but its habit and ecology remain unclear. From Xinhang forest, we now report more specimens of fern-like plants including X. spina and some unnamed plants in several beds. Prominent adventitious roots, spines and secondary xylem indicate that the stems of X. spina are largely procumbent to function as anchorage, absorption and support. Other fern-like plants with distinct roots or multiple slender branches also suggest procumbent habits. Xinhang forest is thus reconsidered as multispecific with a canopy of lycopsid trees and understory of diverse fern-like plants, which are adapted to the disturbed coastal environment. The composition of Xinhang forest may indicate a structural transition of the early forests’ dominator from fern-like plants to lycopsids.


Introduction
Devonian is a key evolutionary period for tracheophytes (vascular plants), including lycopsids, sphenopsids, seed plants and fern-like plants, and they all underwent great development, differentiation and diversity during this time [1].Among them, fernlike plants extending from the Middle Devonian to Carboniferous are composed of iridopteridaleans, pseudosporochnaleans, non-pseudosporochnaleans, rhacophytaleans and stauropteridaleans [2,3].They demonstrate abundant morphological and anatomical characters and show complex phylogenetic relationships [4][5][6], but their living niches are poorly known.
The emergence of forests profoundly remodeled the terrestrial ecosystem and global environment [7][8][9][10].As for the earliest forests in the Devonian, the Middle Devonian (Givetian) Cario and Gilboa forests in New York, NY, USA, are dominated by the arboreous (trees of) fern-like plant Eospermatopteris and progymnosperms including Archaeopteris and/or aneurophytalean taxa [11,12].Of the two Late Devonian forests mainly consisting of trees of lycopsids, one is the Frasnian Svalbard forest from Norway [13] and the other is the Famennian Xinhang forest from China [14,15].
Xinhang forest has thousands of in-situ lycopsid trees of Guangdedendron micrum and is distributed over an area of over 25 hectares.With continual excavation, new fossil plants other than lycopsids were recently discovered from this forest.Among them, Xinhangia spina is a fern-like plant characterized by an aerial stem bearing alternate to triseriate primary branches, simple ultimate appendages and clepsydroid-shaped stele [16].By studying more specimens, this article focuses on X. spina with procumbent stems and other fern-like plants in Xinhang forest, whose habits are discussed in relation to the palaeoenvironment.

Material and Methods
The specimens were obtained from the Leigutai Member (upper part of the Upper Devonian Wutong Formation), at Yongchuan clay mine, which is located in Xinhang Town, Guangde City, Anhui Province, China (Figure 1a,b).The fern-like plants in this study were preserved mainly within mudstone and siltstone, and distributed in both the bottom and the mid-upper beds of Leigutai Member (Figure 1c, vertical red lines), while in-situ roots and stems of lycopsid Guangdedendron micrum are found in almost the whole Leigutai Member (Figure 1c, vertical black lines).Most specimens (Figures 2-6, S1 and S2) were obtained from the two lowest beds of this member (Figure 1c, the two lowest red lines; Figure 1d), which are separated by a thin bed of quartz sandstone.The others (Figure S3) are from the upper bed (Figure 1c, the top red line).The lycopsid Sublepidodendron grabaui Wang and Xu was found near the lower fossil-bearing bed of the Leigutai Member and has been described by Xu et al. [17]. aeoenvironment.

Material and Methods
The specimens were obtained from the Leigutai Member (upper part of the Upper Devonian Wutong Formation), at Yongchuan clay mine, which is located in Xinhang Town, Guangde City, Anhui Province, China (Figure 1a,b).The fern-like plants in this study were preserved mainly within mudstone and siltstone, and distributed in both the bottom and the mid-upper beds of Leigutai Member (Figure 1c, vertical red lines), while in-situ roots and stems of lycopsid Guangdedendron micrum are found in almost the whole Leigutai Member (Figure 1c, vertical black lines).Most specimens (Figures 2-6, S1 and S2) were obtained from the two lowest beds of this member (Figure 1c, the two lowest red lines; Figure 1d), which are separated by a thin bed of quartz sandstone.The others (Figure S3) are from the upper bed (Figure 1c, the top red line).The lycopsid Sublepidodendron grabaui Wang and Xu was found near the lower fossil-bearing bed of the Leigutai Member and has been described by Xu et al. [17].
Steel needles were used to expose the plant morphology.Embedding and polishing techniques were adopted to acquire anatomical information from the permineralized stems.A digital camera and a light microscope were manipulated to take the photographs and Adobe Photoshop CC2018 was used to prepare the figures.All the specimens studied are kept at the Department of Geology, Peking University, Beijing, China.Steel needles were used to expose the plant morphology.Embedding and polishing techniques were adopted to acquire anatomical information from the permineralized stems.A digital camera and a light microscope were manipulated to take the photographs and Adobe Photoshop CC2018 was used to prepare the figures.All the specimens studied are kept at the Department of Geology, Peking University, Beijing, China.Four specimens show stems with adventitious roots (Figures 3a,b and 4a,b).Usually, adventitious roots are arranged one side (Figure 3g, arrows; Figures 3h, 4c-f and S1d,e,g, ar) of the stems.These roots are 0.3-(0.4,n = 18)-0.6mm wide and up to 1.3 cm long and bifurcate occasionally (Figure 3b, arrow 4; Figure 3h, arrows 3,4; Figure 4f, arrow 1).An unusual case shows that the roots seem to be arranged on both sides of the stem (Figure 3f, arrows), but it could not be the original state due to the preservation.Spines could be clearly observed on both upright and procumbent stems (e.g., Figures 2c,e,h and 3h, arrows 1,2; Figure 3i, arrows 5,6; Figure 4e, arrows 1,2; Figure 4f, arrows 2,3) and even the permineralized ones (e.g., Figure 2j, arrows 1-3).

Primary and Secondary Branches
On both the upright and procumbent stems, the primary branches measure 0.5-(1.1,n = 21)-2.0mm wide and up to 9.8 cm long (mean value, n = number of measurements in parentheses, similarly hereinafter), arranged alternately in most cases (Figure 2a, arrows  3a, 4a,b and S1a,d,g, sb), measuring 0.3-(0.7,n = 12)-1.2mm wide and up to 5.8 cm long, and bear vegetative ultimate appendages in alternate arrangement (Figures 4j and 5a,b).Sometimes, such appendages are inserted on the primary branches directly (Figures 2e and S1c, vua).When the primary and secondary branches bear vegetative ultimate appendages, the branches are spineless (e.g., Figure 2e, arrow 8; Figure 5a-c).

Vegetative Ultimate Appendages and Fertile Organs
Vegetative ultimate appendages usually dichotomize once or twice with recurved tips (Figure 5a-c) but sometimes do not dichotomize on the primary (Figures 2e and S1c, vua) or secondary (Figure 4j) branches.Fertile organs are similar to the vegetative ultimate appendages with dichotomy and recurving but bear terminal elongate sporangia in pairs (Figure 2i, arrows 2,3; Figure 5d-g

Other Fern-like Plants
A pair of specimens with only the rooting system preserved along the bedding plane (Figure 6a-c) shows the possible original state when living.The long straight rhizome (Figure 6a,b, white arrows) is 0.6-(0.7,n = 4)-0.9mm wide and up to 6.7 cm long (mean value, n = number of measurements in parentheses, similarly hereinafter).Primary roots occurring on one side of the rhizome are parallel and 0.2-(0.4,n = 16)-0.5mm wide constantly and up to 25 mm long (Figure 6a,b, black arrows).The intervals between adjacent primary roots are 3.7-6.5 mm.Secondary roots are occasionally visible and 0.1-0.2mm (n = 6) wide and up to 6.5 mm long (Figure 6c, arrows 1-6).
Some fern-like plants are associated with Guangdedendron micrum at the bottom of the Leigutai Member (Figure 1c, the two lowest vertical red lines; Figure S2a-l).Several in-situ trunks (Figure S2d-f, arrows) and erect strobili (Figure S2g, arrows) of G. micrum occur on the highwall.Debris of fern-like plants (Figure S2i,j, arrows) and strobili (Figure S2k, arrow) of G. micrum were preserved together.A relatively well-preserved fern-like plant shows several adjacent stems, 1.5-4.0mm (n = 4) wide and up to 11 cm long (Figure S2l, arrows 1-3), bearing possible adventitious roots (Figure S2l, arrow 4) and primary branches.
Fern-like plants are also found at a higher bed in the Leigutai Member (Figure 1c, the top red line; Figure S3a-c).Their numerous branches are preserved with the trunks of Guangdedendron micrum (Figure S3a-c).These branches are 0.8-(1.6,n = 17)-2.3mm wide and over 12 cm long and appear to be perpendicular to the tree trunks.
The root in Figure 6 is tentatively allied to fern-like plants because it differs from the roots typical of the lycopsids, sphenopsids and progymnosperms.The cormose and stigimarian roots of the lycopsids show a swollen base and branched rhizomorph axes, respectively [14].As for Devonian-Permian sphenophyllalean sphenopsids, the adventitious root clusters occur on nodes of the creeping axes (Liu Le et al., in preparation).Relating to the progymnosperms, Archaeopteris shows numerous primary roots diverging from the bases of a single central trunk [12].With regard to the aneurophytalean progymnosperms, unbranched roots envelop the straight or curved horizontal rhizomes [11].The roots of Devonian seed plants are currently unknown; thus, a comparison here is impossible.The seeds, if present in Yongchuan mine, are mostly isolated.Therefore, it is unlikely that the root in Figure 6 relates to the seed plants.The plants with multiple branches in Figures S2 and S3 are assigned to fern-like plants generally because they lack organs, including the following: (1) microphylls and strobili, (2) nodes and internodes, (3) pinnate sporangia and/or megaphylls, (4) seeds and pollen organs.These four groups of vegetative and/or fertile organs characterize the lycopsids, sphenopsids, progymnosperms and seed plants, respectively.

Habits of the Fern-like Plants from Xinhang Forest
Among Devonian fern-like plants, the order Pseudosporochnales contains some treesized members (e.g., Pseudosporochnus, Lorophyton, Pietzschia and Eospermatopteris) and contributes to the earliest forest ecosystems in the Devonian [11,12,18,19], while other fern-like plants are smaller in size and rarely known in relation to the forests [2].In order to clarify the habits of Devonian fern-like plants including Xinhangia, detailed comparisons of relative morphology are given in Table 1.ans [11,18] Eifelian to Frasnian  Quite a few Devonian fern-like plants with roots have been studied in detail (Table 1).Pseudosporochnaleans have a tree-like appearance and their roots are radially arranged around the base of the trunk, like the extant tree ferns or palms [11,18,33], which show great differences from the roots in this study.The aerial roots of Denglongia [27] and Metacladophyton [22] occur below some nodes of stems, while the roots of Xinhangia are born on internodes.Xinhangia's roots are similar to those of Shougangia [3], Rhacophyton [24,25], Melvillipteris [27], Ellesmeris [28] and Protoperidophyton [29], and they are all inserted on the horizontal stems.Similarly, Flabellopteris [30] is interpreted with an erect habit connected to a horizontal rhizome, though evidence of roots is deficient.In the previous study, procumbent stems and roots are undetected in Xinhangia [16].In this study, slender root systems are attached to stems (Figures 3a,b and 4a,b) or found isolated (Figure 6), and some of them have bifurcation (Figure 3b, arrow 4; Figure 3h, arrows 3,4; Figure 4f, arrow 1) or one order of lateral roots (Figure 6c, arrows 1-6), which is rare among Devonian fern-like plants.The roots occur on one side of the stems (Figures 3a,b and 4a,b) or rhizomes (Figure 6) in most cases, indicating that these fern-like plants are, at least partly, procumbent on the ground.The fern-like plants associated with the tree lycopsid Guangdedendron (Figures S2 and S3) are slender and multiply branched, indicating that they may also be procumbent in habit.In the face of the poor drainage and disturbed environment in Xinhang forest, the adventitious roots and well-developed secondary xylem of the stems may together help enhance the absorption of nutrients and/or physical stability in the substance.
In addition to Xinhangia, spines were reported from most iridopteridaleans (e.g., Anapaulia moodyi Berry and Edwards [34], Ibyka amphikoma Skog and Banks [35]) and some other fern-like plants (e.g., Metacladophyton ziguinum Wang and Lin [21]; Tsaia denticulate Wang and Berry [36]), while not in pseudosporochnaleans and rhachophytaleans.In Xinhangia spina, spines are usually observed on the stems and primary branches but are rare on either vegetative or fertile ultimate branches in both previous and present studies.In contrast, some fern-like plants bear spines on ultimate branches (e.g., Anapaulia moodyi, Ibyka amphikoma, Tsaia denticulate), but reasons for their existence are little discussed.The spines of vascular plants are supposed to function as secretory and possible conducting tissue [37], assisting with clinging-climbing [38] or defensing against herbivores, especially for later vertebrates [39,40].For some fern-like plants showing similar habits to Xinhangia, e.g., Denglongia, Ellesmeris, Protopteridophyton and Shougangia, they all lack spines, while their living environments are not known.Considering the disturbed environment to which Xinhang forest adapted [14], we suggest that the spines of Xinhangia may serve as anchors and graspers to help to firmly scramble on and fix to the ground or become tangled with each other for more support.Spines are widespread on procumbent stems with adventitious roots (e.g., Figures 3h and 4e,f), suggesting that these two structures may function together as anchorages to defend the possible periodic flood.The primary branches bearing secondary branches or ultimate appendages grow uprightly for receiving light and spreading spores.When rising up, the plant does not need to grasp the ground, which could explain why the higher orders of branches and ultimate appendages lack spines.

Habitat and Environment
Until now, only a few Devonian forests have been found and studied in detail (Table 2), and they all come from the Laurussia palaeocontinent except for Xinhang forest, in South China (Figure 7).Recently, a Famennian plant assemblage comprising lycopsids, fern-like plants and seed plants was also found from Gondwana palaeocontinent [41].Forests can date back to the Middle Devonian, when pseudosporochnalean trees began to flourish.Eifelian Lindlar assemblage, Givetian Cairo and Gilboa forests from N.Y., USA, [9,12,13,18,42,43] are mainly composed of pseudosporochnalean trees, despite the fact that they are inferred to represent different living environments (Table 2).Just recently, a new study reports the earliest forest in England, four million years older than the one in Gilboa, which is also composed of pseudosporochnalean trees [19].In the Late Devo-nian, structural transition in forests happened according to the existing evidence.The pseudosporochnaleans seemed to retreat from the dominant composition of forests, and instead, lycopsids took place of the main roles of forests in Svalbard of Norway and in Xinhang of China, especially the Carboniferous forests in Euramerica [13,14,[44][45][46].Since the Late Devonian, medium-to small-sized fern-like plants or ferns existed as bushy understory in swamps or mires, i.e., peat-and non-peat-forming wetlands [46].Among them, Late Devonian Rhacophyton dominated the floodplain swamps and the understory in the shade of Archaeopteris or lycopsids [26,[47][48][49], possibly similar to the fern-like plants in Xinhang forest.which is also composed of pseudosporochnalean trees [19].In the Late Devonian, structural transition in forests happened according to the existing evidence.The pseudosporochnaleans seemed to retreat from the dominant composition of forests, and instead, lycopsids took place of the main roles of forests in Svalbard of Norway and in Xinhang of China, especially the Carboniferous forests in Euramerica [13,14,[44][45][46].Since the Late Devonian, medium-to small-sized fern-like plants or ferns existed as bushy understory in swamps or mires, i.e., peat-and non-peat-forming wetlands [46].Among them, Late Devonian Rhacophyton dominated the floodplain swamps and the understory in the shade of Archaeopteris or lycopsids [26,[47][48][49], possibly similar to the fern-like plants in Xinhang forest.Life 2024, 14, 602 14 of 16 The fern-like plants in this research were found from several beds in the Leigutai Member (Figure 1c), suggesting their existence for a long time.Materials from the previous study only contain shoot parts, and elaborate structures such as complete fertile organs attached to branches are preserved [16].Thus, Xinhangia in both previous and present studies, as well as some other fern-like plants (Figures 6 and S2) from the same bed (Figure 1c, the two lowest vertical red lines), are considered as being autochthonous or parautochthonous for the preservation of roots and/or well-preserved aerial branches.The fern-like plants could spread in the lycopsid forest as a possible understory vegetation, since they are often closely associated with the lycopsid trees of Guangdedendron micrum (Figures S2 and S3).These trees without evident canopies permitted the understory plants to receive sunlight.Thus, the vertical stratification of Xinhang forest could be built.The trees of G. micrum grew in a littoral habitat and were prone to be submerged by the frequent coastal flooding [14].Xinhangia is considered as a primitive taxon with simple vegetative and fertile organs [16], which could be related to the disturbed environment for faster growth.As the biggest Devonian forest in the world, Xinhang forest may represent a universal forest structure at that time.Such combination of lycopsids and fern-like plants also seems to be a rudiment of the lycopsid-fern system in the Carboniferous forests [45,51].
The fossil bearing lens consists of mudstone and siltstone, indicating an environment with low energy.Xinhangia in both previous and present studies, as well as the roots in Figure 6, were not associated with the lycopsid trees of Guangdedendron micrum, suggesting that these fern-like plants might have survived in patches.These patches with low energy represented local habitats segregated by numerous lycopsid trees, which were adapted to tidal turbulent environments reflected by quartz sandstones, siltstones and mudstones.

Figure 1 .
Figure 1.Location, stratigraphy of section and outcrop view.(a,b) Locality of the Yongchuan mine in Xinhang Town, Guangde City, Anhui Province, China.(c) Stratigraphic column of the Leigutai Member (Upper Devonian Wutong Formation) at the Yongchuan mine, showing the lithology and

Figure 1 .
Figure 1.Location, stratigraphy of section and outcrop view.(a,b) Locality of the Yongchuan mine in Xinhang Town, Guangde City, Anhui Province, China.(c) Stratigraphic column of the Leigutai Member (Upper Devonian Wutong Formation) at the Yongchuan mine, showing the lithology and occurrence of Guangdedendron (black vertical lines) and the fern-like plants (red vertical lines) in this study.(d) Part view of outcrops at the Yongchuan mine, in which Xinhangia and some other plant fossils were found, showing our group members collecting the plant specimens beside the section.

Figure 3 .
Figure 3. Procumbent and spiny stems of Xinhangia spina from the Yongchuan mine.(a) Three stems (arrows 1-3) with adventitious roots and primary branches bearing secondary branches arranged alternately.(b) Winding stem bearing primary branch bases (arrows 1 and 2) and adventitious roots on one side of stem (arrow 3).Arrow 4 indicating a disconnected root with bifurcation.(c) A long stem with a bifurcation (arrow 1) and alternate primary branch bases (enlarged in i).Another stem (arrow 2) and fertile organ (arrow 3, enlarged in d) in association.(d) Enlargement of the fertile organ in (c) (arrow 3).(e) Winding stem bearing a primary branch base (arrow).(f,g) Enlarged parts in (a) (arrows 1 and 2, respectively), showing adventitious roots on stems (small black arrows).(h) Enlarged part in (b) (arrow 3), showing adventitious roots on one side of stem with spines (arrows 1, 2).Arrows 3 and 4 indicating bifurcating roots.(i) Enlargement of the right part of stem in (c), showing stem bifurcation (arrow 1) and three primary branches or their bases (arrows 2-4).Arrows 5 and 6 indicating spines on stem.

Figure 3 .
Figure 3. Procumbent and spiny stems of Xinhangia spina from the Yongchuan mine.(a) Three stems (arrows 1-3) with adventitious roots and primary branches bearing secondary branches arranged alternately.(b) Winding stem bearing primary branch bases (arrows 1 and 2) and adventitious roots on one side of stem (arrow 3).Arrow 4 indicating a disconnected root with bifurcation.(c) A long stem with a bifurcation (arrow 1) and alternate primary branch bases (enlarged in i).Another stem (arrow 2) and fertile organ (arrow 3, enlarged in (d)) in association.(d) Enlargement of the fertile organ in (c) (arrow 3).(e) Winding stem bearing a primary branch base (arrow).(f,g) Enlarged parts in (a) (arrows 1 and 2, respectively), showing adventitious roots on stems (small black arrows).(h) Enlarged part in (b) (arrow 3), showing adventitious roots on one side of stem with spines (arrows 1, 2).Arrows 3 and 4 indicating bifurcating roots.(i) Enlargement of the right part of stem in (c), showing stem bifurcation (arrow 1) and three primary branches or their bases (arrows 2-4).Arrows 5 and 6 indicating spines on stem.

Figure 4 .
Figure 4. Procumbent stems of Xinhangia spina from the Yongchuan mine.(a,b) Part and counterpart of flexed stem with adventitious roots on one side of internodes, bearing primary branches on the nodes, with secondary branches alternately arranged.(c-f) Enlarged parts in (a,b) (arrows 1-3 in (a), arrow 1 in (b), respectively), showing details of adventitious roots (with occasional bifurcation, arrow 1 in (f)) arranged on one side of stem, dichotomous aphlebia at base of primary branch (arrow 3 in (e), arrow 4 in (f)) and spines (arrows 1 and 2 in (e), arrows 2 and 3 in (f)).(g) Enlarged part in (b) (arrow 2), showing primary branch (the wider axis) with spines (arrows 1-2), bearing a secondary branch (the thinner axis).(h) Primary branch with secondary branches arranged alternately.Arrow 1 indicating enlargement in (j).Arrow 2 indicates an aphlebia at the base of a primary branch.(i) Primary branch with secondary branches arranged alternately.(j) Enlarged part in (h) (arrow 1), showing the whole secondary branch with hook-like vegetative ultimate appendages borne alternately.

Figure 4 .
Figure 4. Procumbent stems of Xinhangia spina from the Yongchuan mine.(a,b) Part and counterpart of flexed stem with adventitious roots on one side of internodes, bearing primary branches on the nodes, with secondary branches alternately arranged.(c-f) Enlarged parts in (a,b) (arrows 1-3 in (a), arrow 1 in (b), respectively), showing details of adventitious roots (with occasional bifurcation, arrow 1 in (f)) arranged on one side of stem, dichotomous aphlebia at base of primary branch (arrow 3 in (e), arrow 4 in (f)) and spines (arrows 1 and 2 in (e), arrows 2 and 3 in (f)).(g) Enlarged part in (b) (arrow 2), showing primary branch (the wider axis) with spines (arrows 1-2), bearing a secondary branch (the thinner axis).(h) Primary branch with secondary branches arranged alternately.Arrow 1 indicating enlargement in (j).Arrow 2 indicates an aphlebia at the base of a primary branch.(i) Primary branch with secondary branches arranged alternately.(j) Enlarged part in (h) (arrow 1), showing the whole secondary branch with hook-like vegetative ultimate appendages borne alternately.

Figure 5 .
Figure 5. Ultimate appendages and anatomy of Xinhangia spina from the Yongchuan mine.(a-c) Vegetative branches alternating by dichotomous ultimate appendages with recurved tips.Arrows indicating such ultimate appendages (a from Figure 3A in [16]).(d) Fertile secondary branch bearing alternate fertile organs with terminal sporangia in pairs (from Figure 4M in [16]).(e) Fertile secondary branch bearing one fertile organ (arrow).(f) Fertile organ dichotomizing into two clusters of sporangia.(g) Enlarged fertile organ in (e) (arrow), which dichotomizes twice and terminates in paired and elongate sporangia.(h,i) Transverse sections of procumbent stem in Figure 2d (at two positions labelled by red star 1 and 2, respectively), showing elongate clepsydroid-shaped primary xylem (arrow) surrounded by radially arrayed secondary xylem.(j,k) Transverse sections of Xinhangia from Figure 7G,K in [16], respectively, showing clepsydroid stele.(l,m) Enlarged parts in (h,i), respectively, showing details of primary and secondary xylem.Arrows 1 and 2 in (l,m) indicating protoxylem poles.Arrows 3-5 in (l) and 3-7 in (m) indicating rays.

Figure 5 . 17 Figure 6 .
Figure 5. Ultimate appendages and anatomy of Xinhangia spina from the Yongchuan mine.(a-c) Vegetative branches alternating by dichotomous ultimate appendages with recurved tips.Arrows indicating such ultimate appendages ((a) from Figure 3A in [16]).(d) Fertile secondary branch bearing alternate fertile organs with terminal sporangia in pairs (from Figure 4M in [16]).(e) Fertile secondary branch bearing one fertile organ (arrow).(f) Fertile organ dichotomizing into two clusters of sporangia.(g) Enlarged fertile organ in (e) (arrow), which dichotomizes twice and terminates in paired and elongate sporangia.(h,i) Transverse sections of procumbent stem in Figure 2d (at two positions labelled by red star 1 and 2, respectively), showing elongate clepsydroid-shaped primary xylem (arrow) surrounded by radially arrayed secondary xylem.(j,k) Transverse sections of Xinhangia from Figure 7G,K in [16], respectively, showing clepsydroid stele.(l,m) Enlarged parts in (h,i), respectively, showing details of primary and secondary xylem.Arrows 1 and 2 in (l,m) indicating protoxylem poles.Arrows 3-5 in (l) and 3-7 in (m) indicating rays.Life 2024, 14, x FOR PEER REVIEW 7 of 17 Class and Order: Incertae sedis.Genus: Xinhangia Yang and Wang 2022 emend.Emended generic diagnosis (with emended and additional diagnoses in brackets): Stems dichotomous [upright or procumbent, with adventitious roots arranged on one side].Primary and secondary branches borne alternately and sometimes in a triseriate pattern.Vegetative or fertile ultimate appendages alternately arranged on secondary branches [or sometimes on primary branches].Vegetative ultimate appendages with recurved tips [usually dichotomizing 0-2] times.Fertile ultimate appendages (=fertile organs) usually dichotomizing 1-2 times to terminate in elongated and paired sporangia.Primary xylem of [upright and procumbent] stems mesarch, clepsydroid-shaped with two

Figure 6 .
Figure 6.Roots of fern-like plant from the Yongchuan mine.(a,b) Part and counterpart of roots.White arrows indicating rhizome and black arrows indicate primary roots.(c) Enlargement of left part in (b), showing details of roots.Arrows 1-6 indicating lateral roots.
size in shape, consisting of an upright trunk with densely inserted branches Main components of forests in Middle Devonian

Table 1 .
Comparisons of Xinhangia with related Devonian fern-like plants.
Life 2024, 14, x FOR PEER REVIEW 11 of 17

Table 1 .
Comparisons of Xinhangia with related Devonian fern-like plants.

Table 1 .
Comparisons of Xinhangia with related Devonian fern-like plants.
Life 2024, 14, x FOR PEER REVIEW 11 of 17

Table 1 .
Comparisons of Xinhangia with related Devonian fern-like plants.

Table 1 .
Comparisons of Xinhangia with related Devonian fern-like plants.

Table 1 .
Comparisons of Xinhangia with related Devonian fern-like plants.

Table 1 .
Comparisons of Xinhangia with related Devonian fern-like plants.

Table 2 .
Comparisons of Xinhang forest with other Devonian forests or tree assemblages.

Table 2 .
Comparisons of Xinhang forest with other Devonian forests or tree assemblages.