Figure 1 A schematic drawing of seeds mechanically protected by lignified woody tissue. (a) Large seeds of some dicotyledonous plants are protected by a woody seed shell. (b) Even small seeds of monocotyledons have lignified pericarps protecting the seed within.

Figure 2 AFM topography traces of a tooth surface (shading indicates depth in nm) around detectable damage following sliding contacts against seed shell fragments. (a) Elaeis guineensis, accompanying graph is a 3D longitudinal profile of the enamel mark, which is just 5 nm deep with a length of ~15 µm. (b) Sacoglottis gabonensis with accompanying cross-sectional profile. This was the most pronounced mark recorded during the experiments. (c) Mezzettia parviflora where the accompanying longitudinal profile highlights deposits of material in the damage zone. (d) Using the AFM as nanomechanical force microscope, the deposit in c is shown to have the elastic modulus of the seed shell of M. parviflora. (e) SEM micrograph of piece of Sacoglottis gabonensis seed shell on end of a flat-head indenter, post-test. (f) Energy dispersive spectroscopy (EDS) maps of this shell fragment, post-test; small amounts of calcium are present. (g) Example of the extremely small enamel chips found adhering to the woody tissue.

Figure 3 Results from sedge nutlet compression tests. (a) Force-displacement plots for compression of differing numbers of nutlets of a sedge, Carex monostachya. Initial fracture occurs at a small force, but further compression releases the endosperm at far higher forces, a pattern amplified as more nutlets are compressed. (b) Images demonstrating catastrophic nutlet failure needed to access the nutrient-rich tissues are a function of both force magnitude and the number of nutlets. High forces are needed for nutlet densification, yet for any given force some nutlets may not fail catastrophically if many nutlets are consumed at once. This implies that processing many nutlets at once requires high forces or repetitive loading.

Figure 4 Micro-CT scans of a Carex monostachya nutlet. (a) A transverse slice and (b) a longitudinal slice through the nutlet; phytoliths show up as green flecks. When segmented (c), large numbers of phytoliths are seen in both seed coat and outer regions of the endosperm, highlighting their position and distribution within the nutlet.