A novel approach for the metric analysis of fern fronds: Growth and architecture of the Mesozoic fern Weichselia reticulata in the light of modern ferns

Abstract

The architecture of primary and secondary pinnae of the fossil fern Weichselia reticulata (C. Stokes et Webb) Fontaine is studied based on 28 large specimens from the upper Barremian La Huérguina Formation of the fossil locality Las Hoyas, Cuenca, Spain. The study of the specimens is performed through a morphometric analysis consisting in a reformulation of the Branching Algorithms method of shape description including measurements (insertion angle, distance between pinnae, first segment length and rachis width) and ratios (interval ratio, branching ratio and tapering ratio). A protocol to relocate isolated fragments of fossil pinnae is also established using the interval ratio (distance between pinnae/ previous distance between pinnae) and insertion angle of the pinnae. All specimens show a similar architecture, having elliptic primary pinnae with a sinuous apically tapering primary rachis and triangular secondary pinnae with pinnules of different morphologies. The analysis of the architecture allows to propose that the position of the frond was plagiotropic and that the frond growth was basiplastic for the petiole head and acroplastic for the primary pinnae. The metric method is applied to explore the architecture of four living fern species ( Angiopteris evecta (Forst.) Hoffm., Matonia pectinata R.Br., Sphaeropteris cooperi (F.Muell.) R.M.Tryon, and Woodwardia unigemmata (Makino) Nakai). Weichselia architecture results extremely ordered and regular in comparison with the primary pinnae variation of the living species.

New insights into the affinities, autoecology, and habit of the Mesozoic fernWeichselia reticulatabased on the revision of stems from Bernissart (Mons Basin, Belgium)

“…(2014) based on measurements of the specimens published in Blanco‐Moreno et al . (2019). This could be an overestimate, given that fronds with a large ratio of petiole width to leaf area (PW 4 /LA) have a lower LMA than expected by the model, and in the case of Weichselia PW 4 /LA is larger than all other ferns in the sample from Peppe et al .…”

“…Other values were obtained from the literature: Weichselia , from personal observation of specimens published in Blanco‐Moreno et al . (2019); Matonia , from Table 1 and Kato (1993); Matonia max., from the maximum stem diameter in Kato (1993); Cyathea , from Table 1, Tanner (1983), and Durand & Goldstein (2001); Psaronius , most frequent stem diameter measurement in Rothwell & Blickle (1982); and Psaronius max., from Table 1 and Rothwell & Blickle (1982).…”

“…They share similar curved stems, dichotomous branching and frond organizations (Blanco‐Moreno et al . 2019). Their anatomy, however, is different: Weichselia has a polycyclic stele while Matoniaceae have solenostelic steles.…”

“…Three variables with biomechanical implications for and of interest in the reconstruction of the plant habit were also calculated using the measurements obtained in Table 1 and in Blanco‐Moreno et al . (2019).…”

“…Once the maximum area of foliage the stem can bear is obtained, the number of possible leaves can be calculated based on the mean area of a single leaf (estimated in Blanco‐Moreno et al . 2019).…”