In this work, the localization, density, morphology and ultrastructure of secretory structures in aerial organs of Flourensia campestris (FC) and F. oolepis (FO) (Asteraceae) by means of a combination of light, fluorescence, transmission (TEM) and scanning electron microscopy (SEM) were examined. The possible role of secretory structures in the production and secretion of the phytotoxic sesquiterpene (-)-hamanasic acid A ((-)HAA) in both species was also assessed. Capitate glandular trichomes were found in all reproductive organs of FC and FO, and were being reported for the first time. These glandular trichomes, typically associated to edges and veins, were of the same type as those already described for vegetative organs, and were abundant in involucral bracts and corolla of tubulose and ligulate flowers. Their density in reproductive organs of both species was similar (ca. 30/mm 2 ) and lower than that found in leaves (ca. 100/mm 2 ) and stems (ca. 160/mm 2 in FC, and up to 650/mm 2 in FO). Glandular trichomes in vegetative organs followed a species-* Corresponding authors. M. P. Silva et al. 926specific pattern of distribution. TEM and SEM observations suggest that each species differs in the way in which secretory materials are released to the outside: through cracks or pores in FC, or through a loose cuticle in FO. Similar inspections of the secretory ducts revealed lipophilic vacuoles localized in subepithelial and epithelial cells, in which secretions accumulated before being transferred to the duct. The presence of wall ingrowths in subepithelial cells suggests that granulocrine secretion operates in these species. Secretory ducts varied in density and diameter among the organs in both species, with the combination being maximal in woody stems. (-)HAA was only detected in surface secreted resins of both species, and its concentration (2D-TLC, GC-FID) was intimately associated with the distribution and density of glandular trichomes in each organ (capitula, leaves, and stems with primary or secondary growth). In addition, no (-)HAA was detected internally in the resins collected from secretory ducts. The composition of these resins showed distinctive profiles for FC and FO, and only four from ca. 30 compounds detected (GC/MS) were shared by both species. In addition to the elucidation of ultrastructural traits, distribution and density of secretory structures in aerial organs of FC and FO, present findings suggest a functional role for glandular trichomes in the secretion of the putative phytotoxic allelochemical (-)HAA.

The effects of natural UV-B radiation on growth, photosynthetic and photoprotective pigment composition of different Salicornia species were analyzed in salt marshes at three different sites along the Americas (Puerto Rico, southern Brazil and Patagonia, Argentina). Plants were exposed to different levels of UV-B radiation for 1-2 years in situ as well as in outdoor garden UV-B exclusion experiments. Different UV-B levels were obtained by covering plants with UV-B opaque (blocked 93-100% of ambient UV-B) and UV-B attenuating (near-ambient) filters (reduced 20-25% of UV-B). Unfiltered plants were exposed to natural irradiance. UV-B filters had significant effects on temperature and photosynthetic pigments (due to changes in PAR; 400-700 nm). The growth of Salicornia species was inhibited after 35 to 88 days of exposure to mean UV-B radiation dosages between 3.6 and 4.1 kJ m(-2) day(-1). The highest number of branches on the main shoot (S. bigelovii and S. gaudichaudiana) and longest total length of the branches (S. gaudichaudiana) were observed in the UV-B opaque treatment. Salicornia species responded to increasing levels of UV-B radiation by increasing the amount of UV-B absorbing pigments up to 330%. Chromatographic analyses of seedlings and adult S. bigelovii plants found seven different UV-B absorbing flavonoids that are likely to serve as UV-B filtering pigments. No evidence of differential sensitivity or resilience to UV-B radiation was found between Salicornia species from low-mid latitudes and a previously published study of a high-latitude population.

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A morphological study of vegetative and reproductive structures was carried out on the tribe Colletieae (Rhamnaceae) composed of six genera and 20 species. The plant habit variation, from trees (up to 8 m high) to prostrate shrubs and tangled bushes, suggests structural differences within the group. All the species have an architecture represented by a sequence of monopodial shoots with limited growth, linked sympodially and with acrotonic dichasial ramification. Foliage leaves are decussate and an axillary complex with two serial meristems is associated with each leaf axil. Ancillary shoots (thorn‐tipped branches, short shoots, secondary branches and reproductive shoots) are present at the nodes. A single structural plan was observed throughout the tribe. Most of the variability may be ascribed to different strategies for adaptation to environmental conditions, specially xeromorphy. Reproductive structures, in terms of inflorescences, also show conspicuous variation throughout the tribe. Three different models are described; in the first two models individual flowers or 3–7 flowered cymes constitute the paracladia of either deciduous monotelic synflorescences, or of synflorescences proliferating into vegetative long shoots; in the third, uniflorous paracladia arise from perennial short‐shoots. Nevertheless, a link within them can be established through steps of truncation, proliferation, reduction and acquisition of rhythmic growth.

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