Nanjinganthus dendrostyla, Fu & Diez & Pole & Ávila & Liu & Chu & Hou & Yin & Zhang & Du & Wang, 2018
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publication ID |
https://doi.org/ 10.7554/eLife.38827.001 |
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DOI |
https://doi.org/10.5281/zenodo.5885032 |
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persistent identifier |
https://treatment.plazi.org/id/0395900F-FFD3-7F69-EAF0-6547FDE0FB7B |
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treatment provided by |
Tatiana |
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scientific name |
Nanjinganthus dendrostyla |
| status |
gen. et sp. nov. |
Nanjinganthus dendrostyla gen. et sp. nov.
Specific diagnosis
the same as the genus.
Description
The flowers are frequently concentrated and preserved in groups on certain bedding surfaces ( Figures 1a–g View Figure 1 and 2a–b), although many of them are preserved as isolated individuals on other slabs.
Flower bud
Aflower bud is preserved as a coalified compression, 6.4 mm long and 3 mm wide, with characteristic longitudinal ribs on the sepals and petals ( Figure 2g). The sepals are estimated to be 1.3–2.2 mm long and approximately 1.8 mm wide ( Figure 2g). The petals (including the eclipsed portion) are estimated to be approximately 3.7 mm long ( Figure 2g). The receptacle/ovary is approximately 3 mm in diameter ( Figure 2g).
Mature flower
The flowers are preserved in various states (including coalification), with cup-form receptacle, epigynous with an inferior ovary, 8.4–10.7 mm in length and 6.8–12.8 mm in diameter, actinomorphic in the bottom and top views ( Figures 1 View Figure 1 a-g, 2a-f,h, 3a-b,d-f, 4a-b,d,g, 5e-i, 6a,f,j,l and 7a,e). The pedicel is approximately 0.76 mm in diameter ( Figure 6a,b View Figure 6 ). Basally fused bracts 0.7–3.7 mm long are observed at the bottom in a few flowers, and a stoma is seen on a bract ( Figures 4 View Figure 4 g-h, 7e,h, and 8h). The receptacle is cup-form, 3–4.8 mm in diameter and 2–4.5 mm high, surrounded by a 0.3 mm thick wall in the bottom and sides, and covered by an ovarian roof from the above ( Figures 2h–i, 4d View Figure 4 , 5h, 6a–b View Figure 6 and 7a,e–f,i View Figure 7 ). Scales are attached on the sides of the receptacle/ovary ( Figures 3a–b, 4a,g–h View Figure 4 , 5i and 7a,e,i View Figure 7 ). The sepals are 1.7–3 mm long and 2.7–4.3 mm wide, with two lateral rib-free laminar areas and usually four longitudinal ribs in the center, and attached to the receptacle rim with their whole bases ( Figures 2 c-f, 3d-f, 4a,b,d-e, 5i,l, 6l, 7e,i, 9a). The elongated epidermal cells are, 44–156 µm x 33–54 µm, with straight cell walls in the middle region, while isodiametric epidermal cells 16–71 µm x 10–54 µm are seen in the lateral laminar areas of the sepals ( Figures 8g View Figure 8 , 9 View Figure 9 h-k and 10d-f). The petals are 3.1–6.6 mm long, 1.9–5.4 mm wide, compressed to only about 11 µm thick, with two lateral rib-free laminar areas, a cuneate base, and 5–6 longitudinal ribs in the center, located inside the sepals on the rim of the receptacle ( Figures 2c–f,h,j, 4a,b,d View Figure 4 , 6a,f View Figure 6 , 7a,e,i View Figure 7 , 8a–f View Figure 8 , 9a– g View Figure 9 ). The ribs are approximately 0.12 mm wide, forking only basally, with elongated epidermal cells with straight cell walls, 32–144 µm x 17–30 µm on the abaxial and 19–72 µm x 13–29 µm on the adaxial ( Figures 8 View Figure 8 a-f, 10a-b). The lateral laminar areas are free of ribs, and each is approximately 1.2 mm wide, with isodiametric epidermal cells 23–64 µm x 18–37 µm ( Figures 8e View Figure 8 , 9g View Figure 9 ). Apossibly immature stoma is seen on one of the petals ( Figure 10c View Figure 10 ). An unknown organ (staminode?) is seen once on the rim of the receptacle ( Figure 6a,m View Figure 6 ). The ovarian roof is horizontal, with smooth integral outer and inner surfaces, 0.14–0.22 mm thick, with a style vertically located on its center ( Figures 4c View Figure 4 , 5h, 6f View Figure 6 and 7a–c,e–g View Figure 7 ). The style is 0.3–0.8 mm in diameter, with lateral branches that make the width of the style 3–6 mm ( Figures 2h–i, 3a–b, 5i–j, 6a,c View Figure 6 and 7a–d View Figure 7 ). The basalmost pair of the lateral branches appear oppositely arranged along the style ( Figures 2h and 3b) while the upper ones appear irregularly arranged ( Figures 2i, 6a View Figure 6 and 7c–d View Figure 7 ). There are longitudinal faint striations on the surface of the style ( Figures 3c and 5j). There are 1.6–3.6 mm long and 1.7–2.2 mm wide round-triangular scales on the sides of the ovary ( Figures 2g, 3b, 4a,g–h View Figure 4 and 5i). Each ovary contains one to three seeds that are 0.65–3 mm x 0.5–1.7 mm, elongated or oval-shaped ( Figures 2f, 5a,c and 6d,f– l View Figure 6 ), hanged on the inner wall of the ovary by a 0.08–0.27 mm wide funiculus ( Figures 5e and 6d–e View Figure 6 ). A micropyle-like depression 0.15 × 0.36 mm is seen on a seed ( Figure 5a,d).
The following figure supplement is available for figure 1:
Figure supplement 1. The type fossil locality of Nanjinganthus, Nanjing in China and isotopic dating.
DOI: https://doi.org/10.7554/eLife.38827.004
Figure 2. Flowers of Nanjinganthus preserved in different states and their details. Bar = 1 mm except otherwise annotated. (A) Numerous flowers preserved on a single slab. Some of the numbered ones are detailed in later figures. PB22222B. Bar = 1 cm. (B) Numerous coalified flowers on the same slab. Some of the numbered ones are detailed in Figure 3d–e. PB22223. Bar = 1 cm. (C) Bottom view of Flower 1 in Figure 2a, showing five sepals (s) and five petals (p) with longitudinal ribs. PB22222B. (D) Bottom view of Flower 2 in Figure 2a, showing four sepals (s) and four petals (p) with longitudinal ribs. PB22222B. (E) Bottom view of the flower in Figure 3f, showing a sepal (s) and three petals (p) radiating from the center, which is obliquely broken to show the relationship among the sepals and petals as in Figure 2j. PB22278. (F) Top view of Flower 1 in Figure 1b with sepals (s), petals (p), and seeds (arrow, enlarged in Figure 6h) inside the receptacle. PB22226. (G) Side view of a flower bud (Flower 1 in Figure 2b) with longitudinal ribs (arrows) on the sepals (s) and petals (p). PB22223. (H) Side view of Flower 1 in Figure 1d, showing a receptacle (h), perianth (black arrows), and a dendroid style (white arrow). PB22224. (I) Side view of Flower 15 in Figure 1e, without sepals or petals. PB22222a. Bar = 1 mm. (J) Detailed view of the flower shown in Figure 2e, showing the arrangement of three petal bases (1-3) inside the sepals (s). These petals bases correspond to the three petals (1-3) in Figure 2e. PB22278.
DOI: https://doi.org/10.7554/eLife.38827.005
The following figure supplement is available for figure 2:
Figure supplement 1. Frequently observed palynomorphs associated with Nanjinganthus .
DOI: https://doi.org/10.7554/eLife.38827.006
Figure 3. Individuals of Nanjinganthus . Bar = 1 mm except otherwise annotated. (A–C, PB22224) (A) Flower 2 in Figure 1d (before the dégagement), showing the petal (1) and style (2) still embedded in the sediments. (B The same flower as in Figure 3a, after dégagement, showing the exposed dendroid style (white arrow) and petal (1), and the scale (sc) on the side of receptacle. (C) Detailed view of the style shown in Figure 3b with faint striations (arrows). Bar = 0.5 mm. (D–E) Flower 2 in Figure 2b after and before the organic material of the sepals (white arrows) and petals (black arrows) were removed for cuticle analysis. PB22223. (F) Bottom view of a flower before processing. Internal details are shown in Figure 2e,j. PB22278. DOI: https://doi.org/10.7554/eLife.38827.007
The following figure supplement is available for figure 3:
Figure supplement 1. Fossil plants associated with Nanjinganthus .
DOI: https://doi.org/10.7554/eLife.38827.008
The following figure supplement is available for figure 4:
Figure supplement 1. Fossil plants associated with Nanjinganthus .
DOI: https://doi.org/10.7554/eLife.38827.010
Figure 5. In situ seeds and flowers. Bar = 1 mm except otherwise annotated. (A) Aseed (outlined) inside the ovary of Flower 16 in Figure 1e. Note the oboval micropyle (black arrow) and funiculus (white arrow). PB22222a. Bar = 0.2 mm. (B) Detailed view of the funiculus (between the arrows) of the seed in Figure 5a. PB22222a. Bar = 0.1 mm. (C) Aseed (detailed in Figure 6i) inside the ovary of Flower 7 in Figure 1e. PB22222a. (D) Detailed view of the oval micropyle (arrows) of the seed in Figure 5a. PB22222a. Bar = 0.1 mm. (E) Aseed (arrow, detailed in Figure 6d–e) inside the receptacle in Flower two in Figure 1b. PB22226. (F, G) Two facing parts of the same flower (Flower 10 in Figure 1e). PB22222a. (H) Top view of a flower with organicallypreserved sepals (s), petals (p) and integral ovarian roof (fr), which is detailed in Figure 4c. PB22279. (I) Side view of a longitudinally split flower with scales (sc) on ovary side, sepals (s), petals (p) and partially preserved style (arrow). PB22489. (J) Detailed view of basal portion of the style (between arrows) arrowed in Figure 5i, with faint longitudinal striations. PB22489. Bar = 0.2 mm. (K) Detailed view of the narrowing base (between arrows) of the rightpetalin Figure 5i. PB22489. Bar = 0.5 mm.(L) Detailedviewofasepalin Figure 5i. PB22489. Bar = 0.2 mm.
DOI: https://doi.org/10.7554/eLife.38827.011
The following figure supplement is available for figure 5:
Figure supplement 1. Flowers of a living angiosperm and its details.
DOI: https://doi.org/10.7554/eLife.38827.012
Holotype
Figure 2d ( PB22222B ).
Isotypes
Figure 6a,f View Figure 6 ( PB22222a ), Figure 7e–i View Figure 7 ( PB22281 ), Figure 5h ( PB22279 ).
Specimens
PB22222-PB22229 , PB22236 , PB22238 , PB22241-PB22243 , PB22245-PB22247 , PB22256-PB22260 , PB22278-PB22282 , PB22489 .
Etymology
dendrostyla , for ‘tree-like’ (dendri -) and ‘style’ (- stylus) in Latin.
Remarks
The receptacle is ‘the axis of a flower on which the perianth, androecium and gynoecium are borne’ ( Stevens, 2018). This is the definition followed here. The important characteristic of the receptacle in Nanjinganthus is its cup form, a form frequently seen in more derived angiosperms according to the APG system.
Adendroid style is seen in ten flowers (four in PB22224, Figures 2h and 3a–b; four in PB2222a, Figures 2i, 5f–g, 6a View Figure 6 and 7d View Figure 7 ; one in PB22282, Figure 7a–c View Figure 7 ; one in PB22489, Figure 5i–j). The repeated occurrences of such an unexpected feature in the specimens of Nanjinganthus underscore its truthful existence. The dendroid-form distal portion of the gynoecium may be branched stigmas in Nanjinganthus . But it is possible that these lateral appendages on the style are actually pollen sac complexes, as are similarly attached on the style in extant Malvaceae ( Judd et al., 1999) . We have performed a meticulous fluorescence microscopic examination of this structure and found no trace of pollen grains, reducing the possibility that these lateral branches are clusters of pollen sacs, which is the case seen in some angiosperms ( Malvaceae ). Abranched distal projection is apparently lacking in all known gymnosperms, but it has been seen some derived angiosperms, such as Passifloraceae, Poaceae and Euphorbiaceae ( Heywood, 1978). One of the advantages of a branched style is the increased receptive area, which is conducive to anemophilous pollination. The occurrence of such feature in Nanjinganthus might suggest that Nanjinganthus had yet not established a close cooperation with animals (insects). However, it is noteworthy that this feature is not seen among extant basal angiosperms sensu APG ( Chase et al., 2016). Considering the extremely early age of Nanjinganthus , we refrain from correlating Nanjinganthus with assumed derived taxa ( Malvaceae and Rosaceae). We hope the future research may shed more light the nature of this part of Nanjinganthus .
We have not seen any trace of the carpels typical of Magnoliales, which were previously believed by some to represent ancestral angiosperms. The seeds are physically enclosed by the cup-form receptacle and ovarian roof in Nanjinganthus . This constitutes the foundation based on which we justify our interpretation of Nanjinganthus as an angiosperm. The lack of carpel typical of Magnoliales cannot prevent Nanjinganthus from being an angiosperm as many angiosperms are actually ‘acarpellate’ ( Heads, 1984; Sattler and Lacroix, 1988). It is noteworthy that, at least in some of basal angiosperms such as Nymphaea (Nymphaeales) ( Taylor, 1991; Taylor, 1996) and derived angiosperms such as Cactaceae ( Boke, 1964), the ovary is inferior and the seeds are attached to the ovarian walls. Whether the ovaries in these taxa share similar derivation pathway is a question worthy of further investigation.
Four terms are used to describe the foliar parts in Nanjinganthus , namely, bract, scale, sepal, and petal. These terms are used according to the following demarcations and definitions. Bracts designate the foliar parts subtending the ovary. The scales are the foliar parts attached to the sides of the ovary. The sepals are those foliar parts attached to the rim of the receptacle with their whole bases. And the petals are foliar parts with narrowing bases attached to the receptacle rim and inside the sepals. Similar occurrence of bracts, sepals and petals is seen in some extant flowers ( Figure 5 —figure supplement 1).
The enclosure of the seeds is fulfilled by the cup-form receptacle from the bottom and the structure here-called ‘ovarian roof’ (preserved complete in Figures 4c View Figure 4 , 5h and 7e–g View Figure 7 , but partially preserved in Figures 2f, 5c and 6f,j,l View Figure 6 ) from the above. The intact ovarian roof is clearly seen in the side view ( Figure 7f–g View Figure 7 ) and in surface view ( Figures 4c View Figure 4 and 5h), in the latter case the seeds inside ovary are fully eclipsed by the ovarian roof. The ovarian roof is partially lost in Figure 6l View Figure 6 , in which a central portion of the ovarian roof broke off revealing one of the seeds inside the ovary. The ovarian roof is almost completely lost (but still with some of its residue) in Figure 6f View Figure 6 , and finally fully lost in Figures 2f and 6j–k View Figure 6 , in which the seeds are plainly visible. This series of varying preservation status of ovarian roof suggests that the ovarian roof has fully enclosed the ovules in its original status, and the loss of ovarian roof and exposure of seeds are artifacts due to preservation.
We cannot recognize the maturity of the ovules/seeds in Nanjinganthus , the length about 1 mm suggests that they are most likely to be seeds rather than ovules, therefore we prefer to use the term ‘seed’ rather ‘ovule’ throughout this paper. The number of seeds in Nanjinganthus is variable. According to our observation, it may be one (not shown), two ( Figure 6f–i View Figure 6 ), or even three ( Figure 6j–k View Figure 6 ).
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