Saxophone stem ontogenesis and functions in Acrocomia aculeata

The underground system known as the saxophone stem produced by seedlings of certain palm species exhibits unique growth patterns and distinctive morphologies. Nascimento e Souza et al. performed morpho-anatomical evaluations of seedlings during the development of the saxophone stem in Acrocomia aculeata, a neotropical oleaginous palm.

Seeds and seedlings of A. aculeata, indicating (on the left) the development phases of the saxophone stem — Seeds and seedlings of *A. aculeata*, indicating (on the left) the development phases of the saxophone stem: (I) growth and curvature of the cotyledonary petiole, (II) expansion and curvature of the ligule and (III) formation of the tuberous region. Longitudinal sections of the seed (A–F) and saxophone stem (K). (A) Embryo inserted within the endosperm of a non-germinated seed; (B) 1 d after germination, showing protrusion of the cotyledonary petiole (arrowhead); (C) 5 d after germination, highlighting the curvature region of the cotyledonary petiole (arrowhead); (D) 10 d after germination; (E) 15 d after germination, showing expansion of the ligule region (arrowhead); (F) 20 d after germination, showing the bending region of the ligule (white arrowhead); (G) 45 d after germination, showing curvature of the base of the saxophone stem (white arrowheads) and the rupture region of the ligule (black arrowhead); (H) 60 d after germination, highlighting the beginning of the formation of the tuberous region (arrow), with upwards growth toward the soil surface – the soil level is indicated by a dashed line; (I) 180 d after germination, showing the base of saxophone stem (white arrow) and the position of the terminal portion of the tuberous region where the senescent primary root is inserted (white arrowhead) – ground level is indicated by a dashed line; (J) 240 d after germination, highlighting the scars of the embryonic leaves (white arrowheads), the remains of the degenerated primary root (white arrow) and the cortical coating (black arrowhead); (K) 240 d after germination, showing the insertion position of the primary root (white arrowhead), and the location of the apical meristem (white arrow). Abbreviations: ar, adventitious root; cp, cotyledonary petiole; ed, endosperm; eo, eophyll; ha, haustorium; le, leaves; li, ligule; me, metaphyll; pr, primary root; s1, first sheath; s2, second sheath; se, seed; sr, secondary root; te, seed coat; tr, tuberous region.

They found the development of the saxophone stem is distinct from other underground systems previously described, and involves three processes: growth and curvature of the cotyledonary petiole, expansion and curvature of the hypocotyl, and expansion of the plumule internodes. The saxophone stem structure represents an important adaptation to dry environments by promoting the burial of both the shoot apex and storage reserves, which facilitates the continuous growth of aerial organs.