Embryology of <i>Ageratum conyzoides</i> L. and A. fastigiatum R.M. King &amp; H. Rob. (Asteraceae)

Ageratum has a complex circumscription, and recent studies have indicated its polyphyletism. The genus has been placed in the tribe Eupatorieae whose embryology is not fully known. Embryological data are conservative and important indicators of phylogenetic relationships and can improve family relationships. This study presents, for the first time in Eupatorieae, embryological data for Ageratum conyzoides and A. fastigiatum. Both species have common features of the family such as a unitegmic anatropous ovule, basal placentation, secretory tapetum, Polygonum megagametophyte, and Asterad embryogenesis. The data obtained reinforce the heterogeneity of the family embryology and show, for the first time, the anther wall development of the monocotyledonous type for Asteraceae. The species studied show also differences between themselves. A. conyzoides has bisporangiated and introrse anthers, conspicuous pappus, and cypselae with trichomes on the ribs, whereas A. fastigiatum has tetrasporangiate and latrorse anthers, pappus absent at maturity, and glabrous cypselae. The data presented support recent phylogenetic molecular studies, suggesting the replacement of A. fastigiatum to another genus along with Gyptidinae.

Compositae; embryogenesis; Eupatorieae; ontogeny; phytomelanin

Authorship

Rafael de Oliveira Franca

Instituto de Biologia, Universidade Federal de Uberlândia, Uberlândia, Minas Gerais, Brasil Universidade Federal de UberlândiaBrasilUberlândia, Minas Gerais, BrasilInstituto de Biologia, Universidade Federal de Uberlândia, Uberlândia, Minas Gerais, Brasil

Orlando Cavalari De-Paula

Renata Carmo-Oliveira

Juliana Marzinek ²2 Author for correspondence: jmarzinek@gmail.com

2 Author for correspondence: jmarzinek@gmail.com

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Figures

Figures (4)

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Figure 1.
Transversal (A-C, F-H) and longitudinal sections (D-E, I, J) of the floral buds and flowers at anthesis of Ageratum. A Young anther of A. fastigiatum, showing the divisions of the primary parietal layer. B Anther of A. conyzoides, note two abaxial sporangia and two remnants of adaxial sporangia. C Detail of the anther wall of A. fastigiatum with persistent epidermis and radial thickening of the endothecium. D-E Simultaneous cytokinesis and tetrahedral tetrad of the microspores of A. fastigiatum. F Anther of the A. fastigiatum under polarized light showing styloid crystals. G General view of the anther of A. fastigiatum showing lateral anther dehiscence. H General aspect of the anther of A. conyzoides showing introrse dehiscence. I-J Detail of the pollen grains of A. fastigiatum with the vegetative cell and two elongated gametes. an anther, arrow: periclinal division of the primary parietal layer, arrowhead stomium, mm microspore mother cell, cr styloid crystal, dy dyad, en endothecium, ep epidermis, ga gamete, ip inner secondary parietal layer, ml middle layer, op outer secondary parietal layer, pe petal, st stigma, ta tapetum, te tetrad of microspores vc vegetative cell

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Figure 2.
Transversal (B-E, I) and longitudinal sections (A, F-H, J-N) of the floral buds and flowers at anthesis of Ageratum. A-B Overview of the flower bud of A. fastigiatum. C Glabrous ribs of A. fastigiatum. D Ribs with trichomes of A. conyzoides. E-F Ovary of A. fastigiatum. G Detail of the asymmetric carpopodium of A. fastigiatum. H Detail of the asymmetric carpopodium of A. conyzoides. I-J Ovule of A. fastigiatum with differentiated endothelium. K Ovule, note early development of the megaspore mother cell below the nucellar epidermis of A. fastigiatum. L Ovule showing the linear tetrad of megaspores of A. fastigiatum. M Detail of the ovule of A. fastigiatum, note chalazal functional megaspore and three microspores degenerating. N Megagametophyte of A. fastigiatum. an antipodes, arrowhead nucellus, ca carpopodium, dm degenerated megaspore, en endothelium, ep epidermis, fd floral disk, fm functional megaspore, ie inner epidermis, im inner mesophyll, mc middle cell, me megaspore, mm megaspore mother cell, ne nectary, nu nucellus, oe outer epidermis, om outer mesophyll, oo egg cell, ov ovule, ow ovary wall, pe petal, rb rapheal bundle, ri rib, st style, sy synergids, tr trichome

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Figure 3.
Longitudinal sections of the seeds of Ageratum fastigiatum (A-D, F-I) and A. conyzoides (E). A-H Immature seeds. A Fertilization of egg cell and middle cell, noted synergid increased density of the cytoplasm and polar nuclei of middle cell fused (arrow). B Early zygote and first cell of the endosperm. C Proembryo resulting from the transversal division of the zygote resulting in an apical cell (ca) and basal cell (cb). D Embryo with four cells, noted q cells originated from a longitudinal division of the apical cell (ca), m and ci resulting from a transverse division of the basal cell (cb). E-F Embryo with 8 cells showing two cells q, two m cells, n and n' derived from a transverse division of ci. G Embryo with 16 cells, which 8 q cells, 4 m, 2 n, o and p result of transversal division of n' cell. H Globular embryo with suspensor. I Mature seed showing embryo with embryo axis straight and two convex planes cotyledons. co cotyledon, ea embryo axis, er endosperm, ga gamete, mc middle cell, oo egg cell, pl plumule, su suspensor, sy synergid, zy zygote

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Figure 4.
Transversal (A, C-D) and longitudinal sections (B, E-I) of the floral buds, flowers, and fruits of Ageratum. A-B Immature fruit of Ageratum showing the early formation of schizogenous space. A A. fastigiatum. B A. conyzoides. C-E Immature fruit of Ageratum, note schizogenous space filled by phytomelanin. C A. conyzoides. D-E A. fastigiatum. F-G Carpopodium of Ageratum. F A. fastigiatum. G A. conyzoides. H-I Floral disk of Ageratum. H A. fastigiatum, note persistent pappus. I A. conyzoides. arrow crashed layer (part of the inner mesocarp, endocarp, and integument), arrowhead phytomelanin, asterisk fibre layer, em embryo, er endosperm, ex exocarp, fd floral disk, im inner mesocarp, in integument, om outer mesocarp, pa pappus

Figure 1. Transversal (A-C, F-H) and longitudinal sections (D-E, I, J) of the floral buds and flowers at anthesis of Ageratum. A Young anther of A. fastigiatum, showing the divisions of the primary parietal layer. B Anther of A. conyzoides, note two abaxial sporangia and two remnants of adaxial sporangia. C Detail of the anther wall of A. fastigiatum with persistent epidermis and radial thickening of the endothecium. D-E Simultaneous cytokinesis and tetrahedral tetrad of the microspores of A. fastigiatum. F Anther of the A. fastigiatum under polarized light showing styloid crystals. G General view of the anther of A. fastigiatum showing lateral anther dehiscence. H General aspect of the anther of A. conyzoides showing introrse dehiscence. I-J Detail of the pollen grains of A. fastigiatum with the vegetative cell and two elongated gametes. an anther, arrow: periclinal division of the primary parietal layer, arrowhead stomium, mm microspore mother cell, cr styloid crystal, dy dyad, en endothecium, ep epidermis, ga gamete, ip inner secondary parietal layer, ml middle layer, op outer secondary parietal layer, pe petal, st stigma, ta tapetum, te tetrad of microspores vc vegetative cell

Figure 2. Transversal (B-E, I) and longitudinal sections (A, F-H, J-N) of the floral buds and flowers at anthesis of Ageratum. A-B Overview of the flower bud of A. fastigiatum. C Glabrous ribs of A. fastigiatum. D Ribs with trichomes of A. conyzoides. E-F Ovary of A. fastigiatum. G Detail of the asymmetric carpopodium of A. fastigiatum. H Detail of the asymmetric carpopodium of A. conyzoides. I-J Ovule of A. fastigiatum with differentiated endothelium. K Ovule, note early development of the megaspore mother cell below the nucellar epidermis of A. fastigiatum. L Ovule showing the linear tetrad of megaspores of A. fastigiatum. M Detail of the ovule of A. fastigiatum, note chalazal functional megaspore and three microspores degenerating. N Megagametophyte of A. fastigiatum. an antipodes, arrowhead nucellus, ca carpopodium, dm degenerated megaspore, en endothelium, ep epidermis, fd floral disk, fm functional megaspore, ie inner epidermis, im inner mesophyll, mc middle cell, me megaspore, mm megaspore mother cell, ne nectary, nu nucellus, oe outer epidermis, om outer mesophyll, oo egg cell, ov ovule, ow ovary wall, pe petal, rb rapheal bundle, ri rib, st style, sy synergids, tr trichome

Figure 3. Longitudinal sections of the seeds of Ageratum fastigiatum (A-D, F-I) and A. conyzoides (E). A-H Immature seeds. A Fertilization of egg cell and middle cell, noted synergid increased density of the cytoplasm and polar nuclei of middle cell fused (arrow). B Early zygote and first cell of the endosperm. C Proembryo resulting from the transversal division of the zygote resulting in an apical cell (ca) and basal cell (cb). D Embryo with four cells, noted q cells originated from a longitudinal division of the apical cell (ca), m and ci resulting from a transverse division of the basal cell (cb). E-F Embryo with 8 cells showing two cells q, two m cells, n and n' derived from a transverse division of ci. G Embryo with 16 cells, which 8 q cells, 4 m, 2 n, o and p result of transversal division of n' cell. H Globular embryo with suspensor. I Mature seed showing embryo with embryo axis straight and two convex planes cotyledons. co cotyledon, ea embryo axis, er endosperm, ga gamete, mc middle cell, oo egg cell, pl plumule, su suspensor, sy synergid, zy zygote

Figure 4. Transversal (A, C-D) and longitudinal sections (B, E-I) of the floral buds, flowers, and fruits of Ageratum. A-B Immature fruit of Ageratum showing the early formation of schizogenous space. A A. fastigiatum. B A. conyzoides. C-E Immature fruit of Ageratum, note schizogenous space filled by phytomelanin. C A. conyzoides. D-E A. fastigiatum. F-G Carpopodium of Ageratum. F A. fastigiatum. G A. conyzoides. H-I Floral disk of Ageratum. H A. fastigiatum, note persistent pappus. I A. conyzoides. arrow crashed layer (part of the inner mesocarp, endocarp, and integument), arrowhead phytomelanin, asterisk fibre layer, em embryo, er endosperm, ex exocarp, fd floral disk, im inner mesocarp, in integument, om outer mesocarp, pa pappus

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Embryology of <i>Ageratum conyzoides</i> L. and A. fastigiatum R.M. King & H. Rob. (Asteraceae)

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[1] 2 Author for correspondence: jmarzinek@gmail.com