Seed morphology of the subfamily pitcairnioideae bromeliaceae and its systematic implications

Scanning electron microscopy (SEM) observations of seed samples of 75 species representing fourteen Pitcairnioideae genera combined with some seed developmental and germination data revealed six classes of seed morphology (the Dyckia type, Puya ferruginea type, Puya hamata type, Fosterella type, Navia type and the Brocchinia type). Overall seed shape, nature of the appendage, presence or absence of visible demarcation between the body and appendage, surface cellular pattern and the permanency of the appendage were especially useful for distinguishing the seed types. Taxonomically, seed characteristics are correlated with other features in indicating a close relationship between i) Encholirium and Dyckia, ii) Fosterella and the Guayana Highland generic group (Ayensua, Connellia and Cottendorfia) and iii) Pepinia and Puya, and within the species of Puya hamata complex. Seed morphology suggests an isolated position for Brocchinia within the subfamily. Phylogenetically, seeds of the Fosterella and Puya ferruginea types represent putative homoplasies due to the reversals and parallelisms in different groups. Other seed types are unique to their lineages. Some putative phyletic transformations of the Brocchinia and Navia type seeds correspond with those of the Tillandsioideae and Bromelioideae, respectively. SEED TRAITS HAVE received a great deal of emphasis in the taxonomic treatments of Bromeliaceae by Harms (1930), Mez (1896,193435), and Smith and Downs (1974, 1977, 1979). Diversity in seed morphology stems from the modifications of the outer seed coat (Poisson, 1877; Szidat, 1922; Netolitzky, 1926). Despite a significant taxonomic role of seed, some basic problems relative to the Pitcairnioideae seed morphology were not examined prior to this study. Caudate, winged and naked seeds have often been recognized in Pitcairnioideae (e.g., Mez, 1934-35; Smith, 1986). These seed types, however, represent only a broad definition without reference to the variation in each type. Further, the developmental alterations of the outer seed coat in naked seeds were not examined in previous works. Phylogenetically, ancestral and derived seed types were not analyzed until the present study. Our goal here was to overcome these deficiencies and assess the morphological variation within the seed types and their systematic imI Received for publication 9 March 1987; revision accepted 5 August 1987. We thank G. K. Brown, S. Gardener, S. Graham, H. Luther, R. W. Read, J. Utley, and an anonymous reviewer for their helpful and critical comments. Also, we thank Usha Varadarajan for typing, Chris Davitt for technical assistance and the curators of GH, MO, NY. This paper is based on GSV's doctoral dissertation. A doctoral dissertation improvement grant from the NSF (BSR 8306999) supported his field research. plications within the subfamily Pitcairnioideae. MATERIALS AND METHODS-Dry seed samples of seventy five species of fourteen genera of Pitcairnioideae were examined using scanning electron microscopy (SEM). The sources of seed material for our study were field collections of one of us (GSV) and the herbarium specimens of GH, MO and NY. For Navia, a taxon with reportedly naked seeds (e.g., Smith and Downs, 1974), our objective was to document some developmental changes of the ovular integument as well as the seed coat. For this purpose, we supplemented the seed analysis with wet-preserved flowers. Two sets of flower material from an individual plant of Navia splendens L. B. Smith were field-collected and wet-preserved in FAA (formaldehyde: acetic acid: ethanol in 0.5:0.5:9). Each collection was made at a six-day interval. Entire ovules and the free-hand cross sections were subsequently transferred to 0.1 M cacodylate buffer and postfixed in OSO4. The specimens were dehydrated through an ethanol series (30, 50, 70, 95, 100%) and critical-point dried in a Bomar critical-point dryer (Varadarajan, 1986; Varadarajan and Gilmartin, 1987). Air-dried seed samples were gold coated in a Technics Hummer-Sputter coater as were the osmium-fixed developmental stages of Navia. The samples were examined in an ETEC Auto