de Moraes Flora Siqueira, de Barros Thais Cury, Paulino Juliana Villela
Programa de Pós-Graduação em Biologia Vegetal Interunidades, Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP), Instituto de Biociências de Rio Claro e Botucatu, SP, Brazil.
Departamento de Biodiversidade e Bioestatística, Instituto de Biociências, Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP), Campus Botucatu, SP, Brazil.
Ann Bot. 2025 Aug 13. doi: 10.1093/aob/mcaf186.
Parkia platycephala, a native Cerrado species, belongs to the tribe Mimoseae (Fabaceae) and is distinguished by its unique capitulum, which comprises two floral morphotypes: seed-producing flowers and nectariferous flowers. The functional roles of these morphotypes remain unclear, prompting us to investigated inflorescence and floral development to explore their evolutionary and ecological significance.
Flowers, inflorescences, and floral buds at various developmental stages were collected and processed for surface analysis (scanning electron microscopy) and anatomical analysis (light microscopy).
We observed the initiation of three floral unit meristems (FUMs), with abortion of the basal FUM likely due to spatial restriction. Floral buds exhibit a subtle developmental gradient, with seed flowers located in the basal and median regions and nectariferous flowers restricted to the apical region of the capitulum. Both morphotypes display an elliptical floral meristem. Sepals arise in a sequential order; petals, simultaneously; antesepalous and antepetalous stamens emerge unidirectionally; and the single carpel develops concurrently with the lateral antesepalous stamens. The stamens are basally fused and adnate to the petals, forming the stemonozone. Polyads in seed-producing flowers contain cytoplasmic content, unlike most polyads in nectariferous morphotype.
The spatial arrangement of floral morphotypes within the inflorescence defines its zonation, with each capitulum functioning as a pollination unit. The congested arrangement of floral buds and pressure exerted by bracts may contribute to developmental peculiarities, including fasciation and merism variation. We hypothesize that the seed-producing flowers function primarily in fertilisation, whereas nectariferous flowers the only morphotypes containing an intrastaminal nectary serve as food reward for pollinator. Additionally, the type of initiation of sepals, reported exclusively in Parkia, underscores its unique floral developmental pattern. Our anatomical and developmental analyses elucidate the reproductive structures of P. platycephala and clarify the functional significance of its floral dimorphism.
扁头球花豆是一种原产于塞拉多的物种，属于含羞草族（豆科），其独特的头状花序使其独具特色，该头状花序包含两种花形态类型：产种子的花和产花蜜的花。这些形态类型的功能作用尚不清楚，这促使我们研究花序和花的发育，以探索它们的进化和生态意义。
收集处于不同发育阶段的花、花序和花芽，进行表面分析（扫描电子显微镜）和解剖分析（光学显微镜）。
我们观察到三个花单元分生组织（FUMs）的起始，基部FUM的败育可能是由于空间限制。花芽呈现出微妙的发育梯度，种子花位于基部和中部区域，产花蜜的花局限于头状花序的顶端区域。两种形态类型均显示出椭圆形的花分生组织。萼片按顺序依次出现；花瓣同时出现；萼前和瓣前雄蕊单向出现；单个心皮与侧生萼前雄蕊同时发育。雄蕊基部融合并贴生于花瓣，形成雄蕊区。产种子花中的多细胞花粉粒含有细胞质内容物，这与产花蜜形态类型中的大多数多细胞花粉粒不同。
花序内花形态类型的空间排列定义了其分区，每个头状花序作为一个授粉单元发挥作用。花芽的密集排列和苞片施加的压力可能导致发育异常，包括扁化和分生组织变异。我们假设产种子的花主要起受精作用，而产花蜜的花作为唯一含有雄蕊内蜜腺的形态类型，为传粉者提供食物奖励。此外，仅在球花豆属中报道的萼片起始类型突出了其独特的花发育模式。我们的解剖学和发育分析阐明了扁头球花豆的生殖结构，并阐明了其花二态性的功能意义。
