Indirect immunofluorescence detection of homogalacturonan epitopes with low (LM19) and high (LM20) levels of esterification in fern petioles and lycophyte stems. Calcofluor White fluorescence (a, e, i, m) shows the full extent of cell walls. (a-d) LM19 is detected in primary cell walls of the vascular bundle of Asplenium rutifolium, while LM20 is restricted to the middle lamellae and intercellular space corners. (e–h) The prevalence of the LM19 epitope over the LM20 epitope is apparent in parenchymatous and collenchymatous tissue of Asplenium rutifolium. (i–l) LM19 is detected in primary cell walls of Asplenium daucifolium, while LM20 is restricted to the middle lamellae and intercellular space corners. (m–p) LM19 and LM20 weakly bind to primary cell walls in the lycophyte Huperzia squarrosum. Abbreviations: par, parenchyma; coll, collenchymatous tissue. No primary antibody controls are provided (d, h, l, p). Scale bars: 40 μm.