Miranthus elegans E.M.FRIIS, P.R.CRANE et K.R.PEDERSEN, 2021

Friis, Else Marie, Crane, Peter R. & Pedersen, Kaj Raunsgaard, 2021, Early Flowers Of Primuloid Ericales From The Late Cretaceous Of Portugal And Their Ecological And Phytogeographic Implications, Fossil Imprint 77 (2), pp. 214-230 : 216-221

publication ID	https://doi.org/ 10.37520/fi.2021.016
persistent identifier	https://treatment.plazi.org/id/03F487DB-FF8F-246F-FC54-FA39FA86C40F
treatment provided by	Felipe
scientific name	Miranthus elegans E.M.FRIIS, P.R.CRANE et K.R.PEDERSEN
status	sp. nov.

Treatment

Miranthus elegans E.M.FRIIS, P.R.CRANE et K.R.PEDERSEN sp. nov.

Text-figs 1–6 View Text-fig View Text-fig View Text-fig View Text-fig View Text-fig View Text-fig

H o l o t y p e. S170155 (Mira sample 100; figured Textfigs 1a, 4c, d, 5c, d).

P a r a t y p e s. S170106 (Mira sample 99), S101263, S101264, S101266–S101268, S153144–S153146, S154535– S154538, S170123, S170125, S266059 (Mira sample 100), S100732 (Mira sample 105).

P l a n t F o s s i l N a m e s R e g i s t r y N u m b e r.

PFN002666 (for new species).

R e p o s i t o r y. Palaeobotanical Collections, Swedish

Museum of Natural History , Stockholm, Sweden ( S) .

E t y m o l o g y. From the elegant shape of the pedicellate flower.

T y p e l o c a l i t y. Mira (40° 25ʹ N, 08° 44ʹ 15ʺ W), about 25 km south of Aveiro GoogleMaps , District of Coimbra, Portugal . T y p e s t r a t u m a n d a g e. “ Argilas de Vagos ” ,

Late Cretaceous (Campanian/Maastrichtian).

D i a g n o s i s. As for the genus with the following addition. Epidermis of pedicel and outer (abaxial) epidermis of calyx composed of cells that each have a central pointed papilla. Trichomes scattered and thin.

D i m e n s i o n s. Length of flower without pedicel and corolla: 0.8–1.0 mm; diameter: 0.7–1.0 mm. Length of flower bud with corolla and without pedicel: 1.5 mm.

Description and comments on the s p e c i e s. The fossil flowers were briefly described and illustrated by Friis et al. (2010, 2011), but not formally named. More material has subsequently been discovered, including a small, informative flower bud. In most flowers the corolla and androecium have been shed ( Text-figs 1a–g View Text-fig , 2a–d View Text-fig ) and the flowers are probably fossilized at a post-anthetic stage. The flower bud has remains of corolla and stamens preserved ( Text-fig. 3a–f View Text-fig ), but unfortunately, internal structures, including the ovary, ovules and parts of the androecium, are not well preserved. These internal structures were partially destroyed during fossilization and are only preserved on one side of the flower, which complicates interpretations of their organisation. The flower bud is assigned to the same species as the post-anthetic flowers based on features of the calyx. A second flower bud from the Mira mesofossil flora is described as a separate species, Miranthus kvacekii , based on epidermal differences from Miranthus elegans .

The flowers are borne on a long, slender pedicel (Textfigs 1a–d, 2d, 3a, b) and lack bracts or bracteoles immediately below the calyx. The pedicel is up to about 0.9 mm long ( Text-fig. 1d View Text-fig ). All of the fossil flowers are isolated and there is no information on inflorescence structure, or how the pedicel may have been attached to the plant.

The flowers are structurally bisexual, actinomorphic, pentamerous and isomerous, about 0.8–1.0 mm long, excluding the pedicel and corolla, and 0.7–1.0 mm in diameter. Including the corolla, but excluding the pedicel, the flower bud is about 1.5 mm long. The calyx is persistent and consists of five imbricate sepals in a single whorl that are fused at the base ( Text-figs 1a–g View Text-fig , 5a, b View Text-fig ). The sepals are narrowly triangular, with the free portion up to about 0.9 mm long, which tapers into a long tip ( Text-fig. 1a–g View Text-fig ). Each sepal is supplied by three distinct vascular bundles, each of which typically appears as a hollow space in transverse sections ( Text-figs 5a View Text-fig , 6a, b View Text-fig ). In some specimens, minor vascular bundles are seen close to the sepal margins. The epidermis of the pedicel, and the abaxial (outer) epidermis of the calyx, is covered by a thick cuticle. The epidermal cells are small, almost equiaxial, thick-walled and typically with a pointed papilla that gives the surface a faint verrucate to spiny appearance. Similar epidermal features are also observed on the outer surface of the young ovaries ( Text-figs 1a–g View Text-fig , 2f View Text-fig , 3c–e View Text-fig , 5a–d View Text-fig , 6a View Text-fig ). Very slender trichomes occur scattered on the outer surface of the sepals ( Text-fig. 2f View Text-fig ). The epidermal cells of the adaxial (inner) epidermis of the calyx lobes are small, equiaxial, thin-walled and covered with a thin cuticle ( Text-fig. 3c–e View Text-fig ). The calyx of the single flower bud is very similar in shape, size and epidermal features to the calyx post-anthetic flowers ( Text-fig. 3a, b View Text-fig ) and the anatomy of all preserved organs is also identical.

There is no trace of corolla and androecium in the supposed post-anthetic flowers. Corolla and androecium were most likely shed together after flowering, which would also be consistent with stamens that were fused to the corolla. The corolla is five-lobed, with imbricate lobes that are free for most of their length ( Text-fig. 3c–e View Text-fig ). They appear united at the base, but the preservation does not allow a fully secure conclusion that they were sympetalous.

The internal structures are preserved on one side of the flower bud, but based on the symmetry of the structures that remain, the androecium can be reconstructed as pentamerous and obhaplostemonous with five antepetalous stamens, which are seen near the base of the flower as stout filaments positioned in front of the petal lobes ( Text-fig. 3c–e View Text-fig ) and near the bud apex as remains of thecae. Smaller structures, interpreted as staminodes, are seen alternating with the petals ( Text-fig. 3c–e View Text-fig ). Both stamens and staminodes appear to be attached to the corolla near the base ( Text-fig. 3f View Text-fig ), which is also consistent with the absence of stamens and stamen bases in the post-anthetic flowers.

Normapolles-type pollen, which is very common on the surface of other Mira mesofossils, is also present on Miranthus flowers. However, in addition, two flowers have another kind of pollen on their surface. In both cases, the pollen is about 16 µm long and triaperturate with very long colpi that reach almost to the poles ( Text-fig. 2g View Text-fig ). Unfortunately, the grains are folded and it cannot be established whether the grains are tricolpate or tricolporate. The tectum is foveolate.

The ovary is semi-inferior and unilocular ( Text-figs 2d View Text-fig , 4a–d View Text-fig , 5a, b View Text-fig , 6a, b, e View Text-fig ). The apical portion of the ovary has a slightly protruding ring with stomata-like openings ( Text-figs 1c View Text-fig , 2b, c View Text-fig ). We think it likely that this zone was nectariferous and that the openings were nectar secreting. In some specimens there appear to be remains of septa in the apical part of the ovary, but these may be invaginations of the ovary wall and they do not reach the centre of the ovary ( Text-fig. 5a View Text-fig ). The style is long, slender ( Text-figs 1e View Text-fig , 4c View Text-fig ), and distinctly five-angled in cross-section with a vascular bundle that extends for the length of the style in each of the angles ( Text-fig. 6c, d View Text-fig ). The style is hollow and the stylar canal is wide along its full length ( Text-fig. 6d View Text-fig ), except near the tip where it is closed ( Text-fig. 6c View Text-fig ). In some specimens, the style is broken, but the specimens available give no indication of different style lengths and the flower is interpreted as homostylous. Placentation is free and central, with a dome-shaped, almost globose placenta,

alternating with the corolla lobes; note verrucate abaxial surface of calyx lobes (ca) and ovary wall (ow) partly distorted and displaced to one side. f: Longitudinal section (orthoslice yz0567) of flower bud showing ovary wall (ow) and insertion of calyx (ca), corolla (co) and stamens (st) on a hypanthium rim. Specimen, Mira 100-S266059 (a–f). Scale bars = 600 µm (a, b), 300 µm (c–f).

borne on a central column ( Text-figs 4a–d View Text-fig , 5a–b View Text-fig , 6a, b, e View Text-fig ). Numerous ovules are densely spaced on the placenta, but not immersed in its surface ( Text-figs 2e View Text-fig , 4a–d View Text-fig , 5a–d View Text-fig , 6b, e View Text-fig ). Ovules are bitegmic and anatropous, about 0.14 mm long, with a reticulate seed surface ( Text-fig. 2e View Text-fig ).

Among the post-anthetic flowers, none has a fully developed fruit. However, some are clearly five-parted, have five valves and are interpreted as young capsules ( Text-fig. 1e, f View Text-fig ). In one specimen the ovary is split open along one of the valves ( Text-fig. 2d View Text-fig ). The epidermal cells of the young capsules are small, equiaxial, and often with tiny papillate projections. Stomata occur scattered over the surface of the calyx lobes and pedicel together with smaller openings that are probably trichome bases. Larger openings are irregularly scattered and are interpreted as schizogenous secretory cavities that are sometimes burst ( Text-figs 1b, c View Text-fig , 4b View Text-fig ).