A New Gnetalean Macrofossil from the Mid-Jurassic Daohugou Formation

Macrofossil evidence has demonstrated a first radiation of gnetophytes in the Early Cretaceous. However, the origin of the diversity of gnetophytes remains ambiguous because gnetalean macrofossils have rarely been reported from pre-Cretaceous strata. Here, we report a new putative gnetalean macrofossil reproductive shoot which possesses opposite phyllotaxy, long linear leaves more or less decurrent and having a prominent midvein and pedicled ovoid-ellipsoid and longitudinally striated chlamydosperms. Our new fossil is different from other known gnetalean macrofossils in the linear-lanceolate leaves with a midvein and pedicled chlamydosperms. As a result, we describe this new macrofossil reproductive shoot as new to science, i.e., Daohugoucladus sinensis gen. et sp. nov. Our new macrofossil displays additional morphological characters distinct from other known Mesozoic and modern gnetalean species and provides additional evidence of the origin and early evolution of female reproductive organs of gnetophytes.


Introduction
Gnetophytes contain three extant monotypic families (Ephedraceae, Gnetaceae and Welwitschiaceae), which possess unusual morphological characters for seed plants, e.g., bisexual cones, flower-like reproductive organs, style-like micropylar tube, unique chlamydosperms with additional envelope(s) partially enclosing the inner ovule and exposing an apical micropylar tube, vessels in the wood anatomy, double fertilization and archegonia lacking in Gnetaceae and Welwitschiaceae [1][2][3][4][5][6][7][8][9]. Since these transitional characters bridge the gap between other gymnosperm groups and angiosperms, emphasis has been placed on this group to seek clues to the origin of angiosperms, and a number of competing hypotheses have been proposed, e.g., euanthial hypothesis, pseudanthial hypothesis, anthophyte hypothesis, neo-pseudanthial hypothesis [10]. Recent phylogenomic and phylotranscriptomic studies have suggested that gnetophytes constitute a monophyletic group which is sister to Pinaceae [11,12]. Despite these advances, the evolutionary history of the unusual morphological characters of gnetophytes has not been critically evaluated.
The enormous diversity is of great significance in unveiling the evolutionary process of female reproductive organs in ephedroid plants. Chlamydosperms are characteristic of gnetophytes, possessing one or two layers of cupules enclosing an inner ovule with a style-like micropylar tube exposed, while female cones of gnetophytes consist of a number of bracts and their axillary chlamydosperms [1,4]. The chlamydosperm of gnetophytes was hypothesized to have originated from a reduced secondary shoot with a basal pair/whorl of foliar organs fused into a cupule enclosing the inner ovule, according to morphology, anatomy, ontogeny and paleobotany [7,8,39,51]. Female cones of gnetophytes have been thought to be compound and homologous to those of conifers [2,51]. Indeed, the female cone of Protoephedraceae is compound and the secondary fertile shoots possess sporophylls distally and bracteoles proximally; Protoephedraceae possessed exposed ovules but no chlamydosperms and were thought to represent the ancestral lineage of eugnetophytes [39]. The origin and evolution of the compound female cone of eugnetophytes were not elucidated until those macrofossils from the Early Cretaceous were discovered recently. A reduction-sterilization evolutionary model has been proposed to explain the origin and evolution of ephedroid female cones: the chlamydosperm is pedicled after its origin and subsequent changes during the evolutionary process include the chlamydosperm losing its pedicel and becoming sessile in the axils of leaves, internodes of the female spike increasingly shortened, leaves modified into bracts and reduction of the lower pairs of bracts [19,31].
However, how this morphological diversity in the Early Cretaceous originated remains arguable due to the lack of macrofossils from earlier geological strata (e.g., the Jurassic). Macrofossil taxa of gnetophytes were rarely found from the Jurassic [40,52]. Here we report a new macrofossil taxon from the Mid-Jurassic Daohugou Formation which provides additional morphological evidence for a better understanding of the evolutionary history of gnetalean plants.

Gnetidae
Daohugoucladus sinensis, gen. et sp. nov.,  Type: NF2020123101 (holotype: NF). Diagnosis: A reproductive shoot having nodes and internodes; leaves opposite, linear to linear-lanceolate, subsessile and possessing a prominent midvein on both sides, decurrent; chlamydosperms terminal on a long and furrowed pedicel, ovoid to elliptic-ovoid, longitudinally striated, truncate or nearly so at the apex with a central projection.
Description: A fossil specimen containing compression of a reproductive shoot, ca. 7.1 cm long (Figures 1 and 5). The unbranched shoot articulate, possessing nodes and internodes (Figure 2a,b). The nodes swollen. The internodes ca. 5 mm long or slightly shorter. Leaves opposite at nodes, linear to linear-lanceolate, 1-2 mm broad, 1.5-4.1 cm long, shorter proximally, longer distally; apex attenuate to lanceolate, base acute and decurrent, subsessile; midvein prominent, impressed on both surfaces (Figure 3a,b); fine longitudinal striations discernible at both sides of the midvein on the abaxial surface ( Figure 3). Chlamydosperms pedicled; pedicel long and axillary to leaves, longitudinally furrowed, straight or slightly curved, ca. 2.2 cm long ( Figure 4a). Chlamydosperms ovoid to elliptic-ovoid, 4-6 × 3-4 mm, having longitudinal ridges and furrows, base acute, apex nearly truncate, the apical portion elevated in the middle forming a micropylar region (Figures 1b and 4b,c). Etymology: The generic name Daohugoucladus is derived from the geological stratum of the fossil (the Daohugou Formation) and the preservation of the reproductive shoot; the specific epithet sinensis means that the fossil is from China.
Type locality: Daohugou Village, Ningcheng County, Inner Mongolia, China. Stratigraphy: The Daohugou Formation, Mid-Jurassic (~165 myr). Remarks: The general morphology of both vegetative and reproductive organs excludes the affinity of our new fossil to ferns and fern allies, cycads, Ginkgo L. and angiosperms, while showing similarity to conifers and gnetophytes. The opposite phyllotaxis tain similarity to modern Podocarpus L'Hér. ex Pers., e.g., linear and midveined, but the reproductive morphology does not support such a relationship, e.g., the pedicled and orthotropous chlamydosperm lacking any subtending bracts (vs. reduced female cones usually with anatropous ovules and more or less fleshy receptacle and epimatium in Podocarpus). Our new fossil is markedly different from Jurassic or earlier conifers in having a single ovulate organ terminal to pedicels (vs. assembled into compound cones or shoots in earlier conifers) [53]. is common in both extant and extinct gnetalean plants, while the long linear leaves are decurrent and possess a prominent midvein, as in conifers. Our new fossil shows a certain similarity to modern Podocarpus L'Hér. ex Pers., e.g., linear and midveined, but the reproductive morphology does not support such a relationship, e.g., the pedicled and orthotropous chlamydosperm lacking any subtending bracts (vs. reduced female cones usually with anatropous ovules and more or less fleshy receptacle and epimatium in Podocarpus). Our new fossil is markedly different from Jurassic or earlier conifers in having a single ovulate organ terminal to pedicels (vs. assembled into compound cones or shoots in earlier conifers) [53]. Daohugoucladus is similar to Juraherba Han et Wang in its leaf morphology (linear and midveined). Juraherba was described as an herbaceous angiosperm from the same stratum [54]. However, the two species are different from one another, e.g., leaves are spirally arranged in Juraherba but opposite in Daohugoucladus, fructifications/chlamydosperms are shorter in Juraherba (2.2-4.1 mm long) than in Daohugoucladus (4-6 mm long). Moreover, the pedicels of the fructifications/chlamydosperms are shorter in Juraherba (14-15.5 mm long) than in Daohugoucladus (ca. 22 mm long) and possess scaly leaves in Juraherba which are lacking in Daohugoucladus. In addition, Juraherba possesses bract-like structures at the base of the fructifications, while Daohugoucladus has no bract-like structures at the base of the chlamydosperms. These differences can clearly distinguish Daohugoucladus from Juraherba. Daohugoucladus is similar to Juraherba Han et Wang in its leaf morphology (linear and midveined). Juraherba was described as an herbaceous angiosperm from the same stratum [54]. However, the two species are different from one another, e.g., leaves are spirally arranged in Juraherba but opposite in Daohugoucladus, fructifications/chlamydosperms are shorter in Juraherba (2.2-4.1 mm long) than in Daohugoucladus (4-6 mm long). Moreover, the pedicels of the fructifications/chlamydosperms are shorter in Juraherba (14-15.5 mm long) than in Daohugoucladus (ca. 22 mm long) and possess scaly leaves in Juraherba which are lacking in Daohugoucladus. In addition, Juraherba possesses bract-like structures at the base of the fructifications, while Daohugoucladus has no bract-like structures at the base of the chlamydosperms. These differences can clearly distinguish Daohugoucladus from Juraherba.
Daohugoucladus resembles gnetalean plants such as Siphonospermum in the opposite phyllotaxy and the chlamydosperms terminal to pedicles but differs from gnetophytes in the leaf morphology. However, leaves of fossil gnetophytes are highly variable, e.g., linear in many ephedroid plants, broad with pinnate venation in Gnetum L. and Constrobilus H.M. Liu et al. [26], divided in Latibractea divisa H.M. Liu et al. [26], strap-shaped in Ephedra multinervia Y. Yang et L.B. Lin [20] and Welwitschia mirabilis Hook. f. [1]. As a result, we think that the midveined leaf shape alone cannot exclude its affinity to gnetophytes.  Daohugoucladus resembles gnetalean plants such as Siphonospermum in the opposite phyllotaxy and the chlamydosperms terminal to pedicles but differs from gnetophytes in the leaf morphology. However, leaves of fossil gnetophytes are highly variable, e.g., linear in many ephedroid plants, broad with pinnate venation in Gnetum L. and Constrobilus H.M. Liu et al. [26], divided in Latibractea divisa H.M. Liu et al. [26], strap-shaped in Ephedra multinervia Y. Yang et L.B. Lin [20] and Welwitschia mirabilis Hook. f. [1]. As a result, we think that the midveined leaf shape alone cannot exclude its affinity to gnetophytes.
The chlamydosperms of Daohugoucladus are pedicled and not assembled into a compound female cone, which reminds us of the female organ of Siphonospermum Rydin et Friis, an ephedroid macrofossil from the Early Cretaceous of the Yixian Formation [28]. Daohugoucladus differs from Siphonospermum in the lengthy linear leaves with a prominent midvein and minor longitudinal striations, and the chlamydosperms having a shorter micropylar tube as a central projection (vs. leaves with parallel veins lacking a midvein, and the chlamydosperm having a longer micropylar tube with an exposed portion 2.5-3.5 mm long in Siphonospermum). The overall shape of the chlamydosperms in our new fossil also resembles gnetalean chlamydosperms from the Early Cretaceous [34,36], but our fossil differs from those Early Cretaceous mesofossil seeds in the seed envelope being undivided and having longitudinal striations (vs. usually three-or four-parted and seed envelope having transverse ridges) [34,36].
The chlamydosperms of Daohugoucladus are ovoid to elliptic-ovoid, which is similar to that of modern Gnetum, but markedly different from those bilateral chlamydosperms in modern Ephedra L. and Welwitschia Hook. f. However, the chlamydosperms of Daohugoucladus are solely positioned at the top of a long pedicel, and not verticillately arranged at nodes and assembled into loose spikes (vs. sessile, verticillately arranged at nodes and assembled into loose spikes in modern Gnetum; refer to Pearson [1] and Maheshwari and Vasil [55]. Our new fossil does not show close similarity to modern gnetophytes except for the opposite phyllotaxy and the presence of the unusual chlamydosperms. The chlamydosperms of Daohugoucladus are pedicled and not assembled into a compound female cone, which reminds us of the female organ of Siphonospermum Rydin et Friis, an ephedroid macrofossil from the Early Cretaceous of the Yixian Formation [28]. Daohugoucladus differs from Siphonospermum in the lengthy linear leaves with a prominent midvein and minor longitudinal striations, and the chlamydosperms having a shorter micropylar tube as a central projection (vs. leaves with parallel veins lacking a midvein, and the chlamydosperm having a longer micropylar tube with an exposed portion 2.5-3.5 mm long in Siphonospermum). The overall shape of the chlamydosperms in our new fossil also resembles gnetalean chlamydosperms from the Early Cretaceous [34,36], but our fossil differs from those Early Cretaceous mesofossil seeds in the seed envelope being undivided and having longitudinal striations (vs. usually three-or four-parted and seed envelope having transverse ridges) [34,36].
The chlamydosperms of Daohugoucladus are ovoid to elliptic-ovoid, which is similar to that of modern Gnetum, but markedly different from those bilateral chlamydosperms in modern Ephedra L. and Welwitschia Hook. f. However, the chlamydosperms of Daohugoucladus are solely positioned at the top of a long pedicel, and not verticillately arranged at nodes and assembled into loose spikes (vs. sessile, verticillately arranged at nodes and assembled into loose spikes in modern Gnetum; refer to Pearson [1] and Maheshwari and Vasil [55]. Our new fossil does not show close similarity to modern gnetophytes except for the opposite phyllotaxy and the presence of the unusual chlamydosperms. Gnetophytes have chlamydosperms with an exposed micropylar tube [4,8]. Our new macrofossil is remarkable in that the chlamydosperm has an apical micropylar region and an extremely short micropylar projection, as also found in many gnetalean chlamydosperms from the Early Cretaceous [36], but unknown in other gymnosperm groups [56]. In addition, the micropylar projection of our new fossil is extremely short and appears truncate. In modern gnetophytes, the opening of the micropylar tube is usually not truncate but oblique [57]. The micropylar tube of modern gnetophytes is fragile and easily broken (pers. observ.) and broken micropylar tubes were frequently found in the Early Cretaceous mesofossil Rothwellia foveata Friis et al. [36]. As a result, it is reasonable to infer that the lack of a prominent micropylar tube is the result of breakage. Gnetophytes have chlamydosperms with an exposed micropylar tube [4,8]. Our new macrofossil is remarkable in that the chlamydosperm has an apical micropylar region and an extremely short micropylar projection, as also found in many gnetalean chlamydosperms from the Early Cretaceous [36], but unknown in other gymnosperm groups [56]. In addition, the micropylar projection of our new fossil is extremely short and appears truncate. In modern gnetophytes, the opening of the micropylar tube is usually not truncate but oblique [57]. The micropylar tube of modern gnetophytes is fragile and easily broken (pers. observ.) and broken micropylar tubes were frequently found in the Early Cretaceous mesofossil Rothwellia foveata Friis et al. [36]. As a result, it is reasonable to infer that the lack of a prominent micropylar tube is the result of breakage.
In the middle portion of the specimen, there is an articulate cylindrical structure adnate to the main shoot and seemingly axillary to the right leaf (Figure 1: s). We believe this structure is the remains of some Arthropoda species, and not organically connected with our new macrofossil plant. We came to this conclusion for a number of reasons: (1) The organic connection between this cylindrical structure and the fossil plant is ambiguous. It In the middle portion of the specimen, there is an articulate cylindrical structure adnate to the main shoot and seemingly axillary to the right leaf (Figure 1: s). We believe this structure is the remains of some Arthropoda species, and not organically connected with our new macrofossil plant. We came to this conclusion for a number of reasons: (1) The organic connection between this cylindrical structure and the fossil plant is ambiguous. It is highly probable that they were just preserved together. (2) There is only one such cylindrical structure preserved together with the fossil plant. (3) It is clear that the fossil plant possesses female reproductive organs and the cylindrical structure would have to be a male reproductive organ if it belongs to the fossil plant. While some may argue that it is similar to the verticillately arranged male cone of Gnetum, it is implausible to have such a strange fossil plant possessing very primitive female reproductive organs like that of Siphonospermum, but with highly specialized male cones similar to modern Gnetum L. on the other hand.
drical structure preserved together with the fossil plant. (3) It is clear that the fossil plan possesses female reproductive organs and the cylindrical structure would have to be male reproductive organ if it belongs to the fossil plant. While some may argue that it similar to the verticillately arranged male cone of Gnetum, it is implausible to have such strange fossil plant possessing very primitive female reproductive organs like that of S phonospermum, but with highly specialized male cones similar to modern Gnetum L. on th other hand. The unusual combination of vegetative and reproductive morphology suggests that this macrofossil belongs to a gnetalean genus that has not yet been described. As a result, we classified the new gnetalean plant as a Gnetidae according to Christenhusz [58] and describe it here as new to science.

Materials and Methods
One fossil specimen was collected from the fossiliferous bed in Daohugou Village, Shantou Township, Ningcheng County, Inner Mongolia Autonomous Region of China, which is near the border of Liaoning Province and Inner Mongolia ( Figure 6). The fossil specimen was a compression with coalified residues embedded in tuffaceous siltstone. The Daohugou Formation contained a Mid-Jurassic flora [54]. Many fossils of plants and animals were found in this fossil bed [52,54,59]. The absolute age of this fossiliferous bed was dated back to the Mid-Jurassic (~164 myr, Callovian) based on Ar40/Ar39 and SHRIMP U-Pb dating methods [52,54,60,61]. This new fossil was studied using a light microscope and digital cameras (Nikon D850, D7100, Olympus TG4 and Sony A7M3). The fossil specimen is deposited in the Herbarium (NF), Nanjing Forestry University, Nanjing, Jiangsu Province of China.
this macrofossil belongs to a gnetalean genus that has not yet been described. As a result, we classified the new gnetalean plant as a Gnetidae according to Christenhusz [58] and describe it here as new to science.

Materials and Methods
One fossil specimen was collected from the fossiliferous bed in Daohugou Village, Shantou Township, Ningcheng County, Inner Mongolia Autonomous Region of China, which is near the border of Liaoning Province and Inner Mongolia ( Figure 6). The fossil specimen was a compression with coalified residues embedded in tuffaceous siltstone. The Daohugou Formation contained a Mid-Jurassic flora [54]. Many fossils of plants and animals were found in this fossil bed [52,54,59]. The absolute age of this fossiliferous bed was dated back to the Mid-Jurassic (~164 myr, Callovian) based on Ar40/Ar39 and SHRIMP U-Pb dating methods [52,54,60,61]. This new fossil was studied using a light microscope and digital cameras (Nikon D850, D7100, Olympus TG4 and Sony A7M3). The fossil specimen is deposited in the Herbarium (NF), Nanjing Forestry University, Nanjing, Jiangsu Province of China.

Discussion
Phyllotaxy is conservative within the gnetophytes. The three living families of gnetophytes usually possess decussate phyllotaxy [1,4], but sometimes ternately whorled phyllotaxy does occur in Ephedra [8,62,63]. Most gnetalean macrofossils do have decussate phyllotaxy, i.e., opposite leaves or branching pattern (Table 1) [18][19][20][21][22][23][24]28,29,38,50]; Alloephedra xingxuei J.R. Tao et Y. Yang is considered as having alternate leaves, which is arguable due to the poor preservation of vegetative characters [17,25]. Our new macrofossil reported here shows that the gnetophytes possess decussate phyllotaxy, so it is reasonable to infer that the decussate or ternately whorled phyllotaxy is conservative and a synapomorphic character of the gnetophytes. Mesozoic macrofossils have shown additional diversity of leaf morphology in the gnetophytes. The three extant families of gnetophytes displays rather stable leaf morphology. Species of Welwitschiacae possess giant strap-shaped leaves with no midvein but multiple parallel veins (Table 1) [1,4]. This leaf pattern was also found in the macrofossils having a Welwitschiaceae affinity from the Early Cretaceous [38,41,42]. Species of Gnetaceae have elliptic to ovoid broad leaves that are pinnately veined, i.e., there is a midvein and a few pairs of lateral veins [1,4,55]. Macrofossils with a Gnetaceae affinity are rare. Khitania S.X. Guo et al. is a male spike from the Yixian Formation, and it preserved no vegetative characters [27]. Protognetum Y. Yang et al. from the Mid-Jurassic Daohugou Formation is a reproductive shoot and possesses ephedroid vegetative characters (e.g., opposite phyllotaxy and linear and parallel-veined leaves) and verticillate sessile chlamydosperms [52]. In Ephedraceae, taxa have opposite or ternately whorled, sessile, linear leaves that are free or fused at the base, forming a sheath with two or three free apical parts; the length of the sheath and the apical free portion is variable among species and normally each leaf has two parallel veins and there is no midvein [1,4]. Early Cretaceous ephedroid macrofossils have shown much higher diversity of leaf morphology than the modern representatives [20,[24][25][26]28,31]. Some of the Cretaceous ephedroid macrofossils possess no leaves, e.g., Ephedra hongtaoi Wang et Zheng [29] and Chengia laxispicata Y. Yang et al. [19]; some have linear, free and parallel-veined leaves, e.g., Liaxia Cao et Wu [24] and Prognetella Krassilov [31]; some others, however, are provided with petiolate broad leaves with pinnate veins (Constrobilus ovata H.M. Liu et al.) [26], or petiolate divided leaves with parallel veins (Latibractea divisa H.M. Liu et al.) [26], or petiolate ovate leaves with forked venation (Spinobractea lanceoleta H.M. Liu et al.) [26], or even strap-shaped leaves with parallel veins similar to those of Welwitschiaceae (Ephedra multinervia Y. Yang et L.B. Lin) [20]. Our new macrofossil in this study has decurrent, long, linear leaves with a prominent midvein and multiple longitudinal striations. The midveined linear leaves of our new fossil show a certain resemblance to that of modern Podocarpus. However, the female reproductive organ of our new fossil is quite different from that of Podocarpus in the pedicled orthotropous ovulate organs (vs. reduced female cones with a basal enlarged receptacle and terminal anatropous ovulate organs) [66]. The leaf pattern of our new fossil is new to gnetophytes and has not been reported in gnetalean fossils. This Mid-Jurassic macrofossil unveils additional leaf diversity of ephedroid plants and furthers our understanding of the early diversification of gnetophytes.
Modern families of gnetophytes have diversified female cones or spikes: Welwitschiaceae possess typical female cones with sessile winged chlamydosperms axillary to bracts [1,4]; Gnetaceae have female spikes with a number of annular structures of modified bracts subtending axillary verticillate chlamydosperms [55]; and Ephedraceae are provided with extremely reduced female cones with only the uppermost pair/whorl of bracts subtending 1-3 sessile chlamydosperms [1,[4][5][6]19]. The female cones/spikes of all three modern families of gnetophytes are thought to be compound and consist of a number of modified bracts subtending axillary chlamydosperms [1,4,5]; the chlamydosperms are specialized reproductive shoots with a basal pair of foliar bracteoles fused into the cupule-like envelope enclosing the inner ovule according to morphological, tetratological, anatomical and ontogenetic evidence [7,8,51,67].
Paleobotanical evidence is pivotal for clarifying the early evolution of female reproductive organs in gnetophytes. Protoephedrites Rothwell et Stockey is a well-preserved macrofossil from the Early Cretaceous and has a compound female reproductive shoot with decussate bracts subtending axillary fertile shoots; the secondary fertile shoots possess one or two pairs of bracteoles and a pair of orthotropous ovules with a short micropylar tube [39]. This fossil displays the hypothesized characters of ancestral gnetophytes and has no typical chlamydosperms but a secondary fertile shoot (Figure 7a) [7,8,19,51], providing solid evidence for the shoot origin hypothesis of chlamydosperms of eugnetophytes. Protoephedrites represents a continuation of stem gnetophytes in the Early Cretaceous. Furthermore, many other Early Cretaceous fossils have demonstrated the first radiation of gnetophytes on earth [68,69], and revealed huge diversity of female cones showing how the chlamydosperms of ephedroid plants were assembled into female spikes/cones and then how these female spikes/cones finally gave rise to the reduced female cones of Ephedra through reduction and modification [19,31,70]. The pedicled chlamydosperm of Siphonospermum represents the primitive form of eugnetophytes (Figure 7b). Later the chlamydosperms became sessile and the internode of the reproductive shoot became progressively shorter, forming loosely arranged female spikes as in Protognetella, in which the bracts were still leaf-like (Figure 7c). Subsequently, leaf-like bracts were modified into broad and short bracts tightly subtending the axillary chlamydosperms, the internodes of those loose female spikes were further shortened, forming increasingly compact female cones with multiple pairs of fertile bracts as in Chengia, Liaoxia and Ephedra cantata Puebla et al. (Figure 7d). Finally, the lower pairs of bracts of these compact female cones became abortive and only the uppermost pair of bracts remained fertile, forming reduced female cones as in Ephedra (Figure 7e) [19,31,70]. The lax female spike of Gnetaceae (Figure 7f) and the compact female cone of Welwitschiaceae (Figure 7g) may have been modified from the female shoot of Prognetella. These basic patterns of fossil ephedroid plants support the reduction and abortion evolutionary hypothesis [19].  (a) ancestral female reproductive shoot displaying megasporophylls with apical naked othotropous ovule (e.g., Protoephedrites [39]); (b) transitional stage displaying the reproductive shoot with pedicled chlamydosperms (e.g., Siphonospermum [28] and Daohugoucladus gen. nov.); (c) transitional stage displaying the female shoot with sessile chlamydosperms axillary to leaves (e.g., Prognetella [31]); (d) transitional stage displaying the spike becoming compact with shortened internodes and modified bracts (e.g., Chengia [19], Liaoningia [21] and Liaoxia [24]); (e) reduced female cone with only the uppermost pair of bracts fertile (e.g., Ephedra [1] and Gurvanella [16]); (f) lax spike of Gnetaceae with (a) ancestral female reproductive shoot displaying megasporophylls with apical naked othotropous ovule (e.g., Protoephedrites [39]); (b) transitional stage displaying the reproductive shoot with pedicled chlamydosperms (e.g., Siphonospermum [28] and Daohugoucladus gen. nov.); (c) transitional stage displaying the female shoot with sessile chlamydosperms axillary to leaves (e.g., Prognetella [31]); (d) transitional stage displaying the spike becoming compact with shortened internodes and modified bracts (e.g., Chengia [19], Liaoningia [21] and Liaoxia [24]); (e) reduced female cone with only the uppermost pair of bracts fertile (e.g., Ephedra [1] and Gurvanella [16]); (f) lax spike of Gnetaceae with verticillately arranged chlamydosperms [1]; (g) compact female cones of Welwitschiaceae with multiple whorls of chlamydosperms [1]. Red star indicates the new fossil plant described in this paper.

Conclusions
A new gnetalean macrofossil, Daohugoucladus sinensis Y. Yang et al., is described from the Mid-Jurassic Daohugou Formation. The new fossil includes a reproductive shoot with long and decussate leaves and pedicled chlamydosperms. Daohugoucladus sinensis is similar to Siphonospermum simplex Rydin et Friis in the pedicled chlamydosperms, but differs from the latter in the long and mid-veined leaves. Both Daohugoucladus sinensis and Siphonospermum simplex display the primitive reproductive morphology of gnetophytes in the form of pedicled chlamydosperms. The finding of Daohugoucladus sinensis is important for a better understanding of the early evolution of gnetophytes because it extends the age of this primitive morphology back to the Mid-Jurassic.  Data Availability Statement: All data and materials used in this study are included in this paper.