Floral ontogeny of Tachigali (Caesalpinioideae, Fabaceae) species

Abstract

Background: The present ontogenetic study reveals variations throughout floral development in three morphologically representative species from the genus Tachigali, allowing a better understanding of floral organs diversity, flower symmetry and their homologies, especially in Fabaceae, a diverse family that exhibits a wide variation in floral architecture. Tachigali (Caesalpinioideae) corresponds to an important Neotropical legumes tree genus with 58 species in Brazil. Species of the genus Sclerolobium Vogel were incorporated in its circumscription, increasing the diversity of its floral morphology.

Methods: This work aims to perform an ontogenetic study of T. denudata, T. paratyensis and T. spathulipetala, morphologically representative species of Tachigali, in order to describe the floral development and to better comprehend the floral morphology varieties among the species, using scanning electron microscopy.

Results: We found the studied species to have floral buds with acropetal and helical development along the inflorescence axis; sepals and petals with helical development, varying the position of the primordia in the bud, according to the different species; stamens with unilateral development and carpel with adaxial curvature. These data correspond to original records of Tachigali ontogeny and contribute to an improved understanding of floral morphology and symmetry with data related to the zygomorphic and early development of the sepals and petals.

Keywords: Floral development; Floral symmetry; Sclerolobium.

Figure 1. Tachigali paratyensis inflorescence.

Apex showing the acropetal and helical growth of flower buds (1–28). Bar: 200 µm.

Figure 2. Floral ontogeny of Tachigali paratyensis.

(A–G) Inflorescence axis at the top of the images. (A–D) Bracts removed; (E–G) bracts and sepals removed. (A) Floral primordium at the base of the bract; observe the formation of the first sepal (yellow) in the abaxial position. (B) Two floral primordia with three sepals initiated (yellow 1–3); emergence of simple trichomes indicated by arrowhead. (C) Three sepals in formation (yellow 1–3) and the primordia of the fourth (yellow 4) and fifth (yellow 5); simple trichomes indicated by arrowhead. (D) All sepals already set in the flower bud (yellow 1–5). (E) First sepal (yellow 1) removed, the other sepals (yellow 2–5) are arranged as quincuncial aestivation pattern. The dashline indicated the position of the five sepal under the sepals 2 and 3. (F) Five petals in formation (green 1–5), as well as the first stamen in abaxial position (purple 1) and the second stamen primordia (asterisk) carpel development initiation (orange). (G) Establishment of five petals (green 1–5) and antesepalous stamens (purple 1–3); carpel in development (orange). Bar: A, B, D and E = 20 µm; C and F = 50 µm.

Figure 3. Floral ontogeny of Tachigali paratyensis.

(A–C) Inflorescence axis at the top of the images. (A, B) Bracts and sepals removed. (C–F) Bracts, sepals and petals removed; (G) bracts, sepals, petals, and stamens removed. (A) Establishment of petals (green 1–5) and antesepalous whorl of stamens (purple 1–3), and the first antepetalous stamen primordium (blue); carpel in development (orange) with emergence of the carpel cleft (arrowhead). (B) Petals expanding (green 1–5); antesepalous whorl of stamens (purple 1-3) and antepetalous stamens primordia (blue 4); and carpel elongating (orange) with the closure of the carpel cleft (arrowhead). (C) Development of antesepalous stamens (purple 1–3) and antepetalous stamens primordia (blue 4–6); carpel elongating (orange). (D) Stamen development (purple 1–3; blue 4–6); carpel curvature (orange) towards the adaxial portion. (E) Established double whorl of stamens (purple 1–3; blue 4–6); style bent towards the adaxial portion (orange). (F) Side view of floral bud; arrowhead indicating the double whorl of stamens (purple and blue). (G) Side view of the flower bud showing only the gynoecium (orange). Bar: A–D = 100 µm; E = 500 µm; F, G = 200 µm.

Figure 4. Floral ontogeny of Tachigali denudata (A–F).

(A–F) Inflorescence axis at the top of images. (A–C) Bracts removed. (D–F) Bracts and sepals removed. (A) Floral primordium at the base of the bract; observe the primordia of the first and second sepal (yellow 1–2). (B) Emergence of the third, fourth and fifth sepals (yellow 3–5). (C) Five sepals (yellow 1–5); development of trichomes in the abaxial surface of the sepals (arrowhead). (D) Primordia of the five petals (green 1–5); primordia of the antesepalous stamens (purple 1–3); carpel development initiation (orange). (E) Filiform petals established (green 1–5); carpel in development (orange) with emergence of the carpel cleft (arrowhead). (F) Filiform petals established (green 1–5); carpel elongating (orange) with closure of the carpel cleft. Bar: A, B, D–F = 20 µm; C = 100 µm.

Figure 5. Floral ontogeny of Tachigali spathulipetala (A–D) and Tachigali denudata (E, F).

(A–D) Inflorescence axis at the top of images. (A, B) Bracts and sepals removed. (C–E) Bracts, sepals and petals removed. (F) Bracts, sepals, petals, and stamens removed. (A, B) Filiform and spatulate petals (green 1–5); an antepetalous stamen primordium (blue 6); and carpel in development (orange). (C) Antepetalous stamens established (purple 1–3); antepetalous stamen primordia (blue 4–6); carpel in development (orange) with emergence of carpel cleft. (D) Anthers of the antesepalous stamens expanding (purple 1–3); and antepetalous stamen primordia (blue 4–6); and carpel (orange) elongating. (E) Anthers already formed on both androecium whorls (purple 1–3, blue 4–6); connective extension (arrowhead) style bent towards the adaxial portion. (F) Side view of the flower bud, only the gynoecium (orange); arrowhead pointing to stigma. Bar: A–D = 100 µm; E, F = 200 µm.