Jorge Ernesto Araujo Mariath

1 IntroductionBromeliaceae is an early diverging monocot family within the order Poales (Bouchenak-Khelladi et al., 2014). Traditionally, the family was divided into three subfamilies based mainly ...

Background and Aims: Understanding post-seminal development is essential for species conservation and provides key insights into reproductive biology and macroevolution. Despite their remarkable structural diversity among monocots, seedlings remain an understudied developmental stage, although they are critical for juvenile sporophyte survival and establishment. In Bromeliaceae, one of the major adaptive radiations of monocots, knowledge of seedling development remains fragmented and taxonomically biased. This study comparatively characterizes the ontogeny and morphoanatomy of bromeliad seedlings, providing the first broad phylogenetic assessment for the family. Methods: A total of 33 species from 16 genera representing seven subfamilies were analysed, including Brocchinia, the sister genus to all other bromeliads, as well as rare, endemic and threatened lineages, such as Hechtioideae and Navioideae, that had never been sampled before. Post-seminal development was monitored using light and scanning electron microscopy. Characters were optimized on a consensus supertree using maximum parsimony and maximum likelihood. Key Results: We described and compared 31 informative morphological, micromorphological and anatomical characters of the eophylls, cotyledons and roots. Our analyses indicate that a compact, early-photosynthetic cotyledon and peltate trichomes are plesiomorphic features of the family. In contrast, a laminar cotyledonary hypophyll and uniseriate glandular trichomes represent derived conditions shared by most lineages. Anatomical features, including the presence of a water-storage hypodermis, stomatal position and variation in sclerenchyma associated with vascular bundles, also show taxonomic and ecological significance. Conclusions: Through a phylogenetically representative analysis of seedling ontogeny, anatomy and micromorphology, including previously unsampled taxa, we provide the first evolutionary assessment of this life stage across major lineages of Bromeliaceae. Our findings establish a novel comparative framework for future investigations of seedling development and evolution in Bromeliaceae and other tropical monocots, while expanding current understanding of the evolution of adaptive strategies associated with vegetative organs in the family.

Bromeliaceae exhibits significant pollen diversity. Within the family, pollen grains are dispersed either as monads or tetrads and may be monosulcate, bi-, tri-, tetra-, or pantoporate, or even inaperturate. Ornamentation includes reticulate, foveolate, microreticulate, perforate, or psilate patterns. Additional variations are observed in the margins of the apertures and in the exine deposition on the aperture membrane. In general, pollen grains are relatively well-documented in Bromeliaceae. However, there is a lack of systematization and organization to provide a comprehensive and integrated understanding of its pollen structure. This study aims to conduct a general review of pollen morphology in Bromeliaceae, analyze character diversity based on the current phylogeny of the family, and propose the ancestral states of pollen traits. The study sampled 127 species from 47 genera, supplemented by literature data of 220 species (from 14 additional genera). Together, this dataset encompasses over 70% of the genera in the family and includes species from all subfamilies. Ancestral character states were inferred through a maximum parsimony approach. The identified ancestral states include monads as the dispersal unit, heteropolarity, bilateral symmetry, medium size, a basic elliptical shape, monosulcate pollen, a simple sulcus type, margin type III (Puya type), and reticulate ornamentation. Bromelioideae is eurypalynous, with a predominance of biporate pollen grains in Core Bromelioideae. Tillandsioideae is considered stenopalynous, characterized by monosulcate pollen grains. However, the subfamily shows considerable variation in sulcus types. Pitcairnioideae is also stenopalynous and monosulcate but exhibits significant variation in the sulcus and ornamentation. The remaining subfamilies display less variation and are stenopalynous. This study provides a comprehensive overview of pollen diversity in Bromeliaceae and highlights its evolutionary patterns, offering a basis for further research on character evolution and systematics of the family.

Bromelioideae exhibits high variability in pollen characters and is therefore eurypalynous. Palynological studies have described numerous genera within the subfamily, contributing to a more precise circumscription at generic and infrageneric levels. However, most studies have focused on surface analyses or observations of the sporoderm in pollen grains lacking cytoplasmic content (lux obscuritas microscopy). As a result, characters describing internal structures that are not resistant to acetolysis, such as the intine, have been less frequently addressed. This study aimed to describe the pollen types found in Bromelioideae by analysing the sporoderm surface and stratification patterns using a combination of anatomical techniques, acetolytic treatment, and scanning electron microscopy. The results confirmed the palynological diversity of Bromelioideae, revealing variations in pollen size, shape, dispersal unit, aperture number, ornamentation, and infratectum types. Differences were also observed in sporoderm stratification, aperture type, and aperture margins. The intine exhibited remarkable diversity, being predominantly stratified into three layers, with distinct patterns observed in some species. A structurally unique feature was identified in diporate grains, here referred to as the pseudoannulus.

Several species complexes of Dyckia s.s. have been investigated in recent years, with the taxonomy of the genus regarded as one of the most challenging within the family. In this study, we propose the circumscription of the Dyckia remotiflora complex and present a taxonomic-nomenclatural revision for the included taxa: D. remotiflora var. remotiflora, D. remotiflora var. vaginosa stat. nov., D. choristaminea, D. neojonesiana sp. nov., and D. pontesii. Additionally, we propose elevating the taxon D. tandilensis stat. nov. to species status and synonymizing D. remotiflora var. angustior in D. tuberosa, both excluded from the complex. The complex is analyzed in terms of distribution and habitat, conservation, evolution and phylogeny, natural hybrids, morphology and taxonomy, and a key for identification is provided. For each taxon within the complex, we present taxonomic treatment, nomenclatural types for accepted names and synonyms, etymology, distribution and habitat information, as well as morphological and taxonomic observations.

The taxonomic circumscription of many bromeliad species is doubtful, and this is the case for Dyckia alba. We explore unusual characters from several data sources, such as macromorphological, floral micromorphological, floral anatomy, and palynological, to more accurately circumscribe D. alba. In light of these data, we concluded that the originally proposed circumscription for D. alba covers two independent lineages that should be treated as two species. As a result, we propose a less comprehensive circumscription for D. alba and the segregation of a new species, described here as Dyckia witeckii. Morphological descriptions of the vegetative and reproductive organs are presented for both species, as well as little-explored morphological features in Dyckia, such as the micromorphology of perianth trichomes and pollen, along with the floral anatomy. We also provide, for both species, data on geographic distribution and habitat. Comparative morphoanatomy proved to be an important tool in this study and has great potential for application in taxonomic studies of Bromeliaceae.

Dorstenia species are characterized by their distinctive inflorescence, the coenanthium, a fleshy discoid receptacle that contains staminate or pistillate flowers. Despite being of great importance due to the endangered status of some Dorstenia, few species have been extensively studied, leaving many aspects of their reproductive biology and evolutionary relationships unclear. This study aimed to expand our understanding of Neotropical Dorstenia species, focusing on less-explored aspects. Using light and scanning electron microscopy, we analysed the inflorescences of seven species across all Neotropical sections and conducted ancestral character reconstruction to verify the phylogenetical significance of specific traits. Results showed that aerenchyma development in pistillate flowers may play a role in fruit dispersal through ballistic ejection. Additionally, the secretory structures within the coenanthium, both external and internal, probably serve the dual purpose of attracting pollinators while also providing protection against potential damage from them, although the exact pollination syndrome remains uncertain due to conflicting data. The reproductive characteristics of the Neotropical Dorstenia differ among the three sections, with the late-diverging Emygdioa members exhibiting dioecious coenanthia, implying a transition from mixed-monoecious to dioecious inflorescences in Dorstenia.