Histological description of Saxifraga paniculata leaves with special focus on structures that release CaCO₃

Abstract

Saxifraga paniculata is a subalpine succulent perennial plant arranged in a rosette that is usually found in shallow soil among limestone rocks. Stereoscopic, light and scanning electron microscopy were used to describe the anatomical structure of S. paniculata leaves, paying special attention to structures related to CaCO 3 (calcium carbonate) release. Anomocytic stomata are unevenly distributed on each leaf face, being absent in the lower third. The basal leaf margin presents translucent pluricellular trichomes of variable length and width. Towards the apical margin, trichomes become teeth. Both trichomes and teeth are completely covered with whitish CaCO 3 crystals. Each tooth has a circular cavity connected to a single hydathode through pores. Clearing treatment revealed camptodromous leaf venation. Anatomical structure shows a bifacial cross-section with spongy mesophyll cells at basal part, becoming heterogeneous at the apex with palisade mesophyll on the adaxial face. Hydathodes are epithematic and connected to outer cavities via two kidney-shaped guard cells showing large substomatal cavity. The epithem is surrounded by a thickened sheath and is formed of highly packed elongated cells with interspersed tracheary elements. CaCO 3 deposits consist of microscopic crystals with varying geometries, of which the rhombus is the basic unit.

Revisiting an ecophysiological oddity: Hydathode‐mediated foliar water uptake in Crassula species from southern Africa

“…Most of the species in this geographical range belong to subgenus Disporocarpa , which tends to extend beyond the GCFR (Bruyns et al, 2019). The white mineral crust that we observed on the hydathodes of C. multicava and C. ovata (Figures 3–5) has generally been regarded as a sign of frequent guttation (Chen & Chen, 2005; Mehltreter et al, 2022; Michavila et al, 2021; Tölken, 1974) and has also been noted in other species of subgenus Disporocarpa such as C. lactea (Whittaker, 2015). Under conditions of high soil moisture and low transpiration, these Crassula species most likely experience guttation, which is known to promote water flux and transport of nutrients when transpiration is limited, while preventing excessive water accumulation and detrimental mesophyll flooding (Bellenot et al, 2022; Cerutti et al, 2019; Feild et al, 2005).…”

“…Most of the species in this geographical range belong to subgenus Disporocarpa, which tends to extend beyond the GCFR (Bruyns et al, 2019). The white mineral crust that we observed on the hydathodes of C. multicava and C. ovata (Figures 3-5) has generally been regarded as a sign of frequent guttation (Chen & Chen, 2005;Mehltreter et al, 2022;Michavila et al, 2021;Tölken, 1974) and has also been noted in other species of subgenus Disporocarpa such as C. lactea (Whittaker, 2015).…”