RESURRECTION OF THE GENUS ENDOLEPIS AND CLARIFICATION OF ATRIPLEX PHYLLOSTEGIA (CHENOPODIACEAE)

The genus Endolepis was first described by Torrey in 1860 with E. suckleyi (E. dioica [Nutt.] Standley) as the only species, noting that it differed from species of Atriplex by the presence of perianth parts in the female flowers. Later, Standley described two additional species: E. covillei and E. monilifera. H. M. Hall and Clements merged Endolepis with Atriplex because they thought that the presence of perianth parts in female flowers was variable in Atriplex phyllostegia. It is now clear that this observation was erroneous; A. phyllostegia never has perianth parts in its female flowers. The plants that they examined that had female flowers with perianth parts were specimens of Endolepis covillei; only those with female flowers devoid of perianth parts were specimens of Atriplex phyllostegia. These two taxa differ by several other major attributes including differences in leaf shape, leaf anatomy, fruiting-bract size and shape, fruiting-bract appendages, and flowering habit, and therefore justify taxonomic separation. Also, because the presence of perianth parts in bracteolate female flowers is a rare attribute in the tribe Atripliceae, consistently absent in Atriplex, but always present in Endolepis, the retention of the genus Endolepis, separate from Atriplex, is deemed warranted. We propose that the genus Endolepis comprise two species, E. dioica and E. covillei. The species named E. monilifera by Standley is based on a specimen of Atriplex serenana Nels.     

ARE TRIOECY AND SEXUAL LABILITY IN ATRIPLEX CANESCENS GENETICALLY BASED?: EVIDENCE FROM CLONAL STUDIES

Prior studies have alternatively considered floral phenotypes in Atriplex canescens as trioecious (having three sexual genders) and/or dioecious and having a “leaky genetical switch.” Clones transplanted from three populations and grown in common gardens reveal the existence of two distinctly different genetic controls regulating gender expression. In some clones gender is fixed as male (staminate) or female (pistillate), while in other clones gender varies, ranging from a mixture of male and female ramets to simultaneous hermaphrodites with various proportions of male and female flowers. For clones which vary their sex expression, variation occurs within irrigation treatments, between treatments and over time, as a consequence of the combined effects of genotype plus environment. The magnitude of sex change is also a product of the interaction of genetics and environment. Some clones have been repeatedly examined for 20 years.     

Visual discrimination between two sexually deceptive <Emphasis Type="Italic">Ophrys</Emphasis> species by a bee pollinator

Almost all species of the orchid genus Ophrys are pollinated by sexual deception. The orchids mimic the sex pheromone of receptive female insects, mainly hymenopterans, in order to attract males seeking to copulate. Most Ophrys species have achromatic flowers, but some exhibit a coloured perianth and a bright, conspicuous labellum pattern. We recently showed that the pink perianth of Ophrys heldreichii flowers increases detectability by its pollinator, males of the long-horned bee Eucera berlandi. Here we tested the hypothesis that the bright, complex labellum pattern mimics the female of the pollinator to increase attractiveness toward males. In a dual-choice test we offered E. berlandi males an O. heldreichii flower and a flower from O. dictynnae, which also exhibits a pinkish perianth but no conspicuous labellum pattern. Both flowers were housed in UV-transmitting acrylic glass boxes to exclude olfactory signals. Males significantly preferred O. heldreichii to O. dictynnae flowers. In a second experiment, we replaced the perianth of both flowers with identical artificial perianths made from pink card, so that only the labellum differed between the two flower stimuli. Males then chose between both stimuli at random, suggesting that the presence of a labellum pattern does not affect their choice. Spectral measurements revealed higher colour contrast with the background of the perianth of O. heldreichii compared to O. dictynnae, but no difference in green receptor-specific contrast or brightness. Our results show that male choice is guided by the chromatic contrast of the perianth during the initial flower approach but is not affected by the presence of a labellum pattern. Instead, we hypothesise that the labellum pattern is involved in aversive learning during post-copulatory behaviour and used by the orchid as a strategy to increase outcrossing.     

FLOWER DEVELOPMENT IN DIOECIOUS SPINACIA OLERACEA (CHENOPODIACEAE)

Spinacia oleracea (Chenopodiaceae) is a potential model system for studies of mechanisms of sex expression and environmental influences on gender in dioecious species. Development of the male and female flowers and inflorescences of spinach were studied to determine when the two sex types can be distinguished. We found that female inflorescence apices are significantly larger than those of the male. Flower primordia are similar in size prior to perianth initiation, but the male primordia develop at a faster rate. Another distinguishing feature at this early stage is the larger bract subtending the female primordium. The two flower types become readily distinguishable when the perianth initiates. Male flowers produce four sepals and four stamens in a spiral pattern in close succession. Female flowers produce two alternate perianth parts that enlarge somewhat before the gynoecium becomes visible. There are no traces of gynoecia in male flowers or of stamens in female flowers. We propose that plant sex type is determined before inflorescence development, prior to or at evocation.     

EVOLUTIONARY STUDIES OF ATRIPLEX: CHROMOSOME RACES OF A. CONFERTIFOLIA (SHADSCALE)

Atriplex confertifolia (Torr. and Frem.) S. Wats., a species endemic to western United States, occurs as 2n, 4n, 6n, 8n and 10n chromosome races. In the Great Basin, diploids occur altitudinally above the upper levels of Pleistocene lakes; the polyploids are in valley bottoms and sides. Diploids are larger in all respects than tetraploids, hexaploids, and octoploids. Decaploids are the most robust of all. Diploids can be distinguished in early seedling stages by having broader leaves and shorter internodes than polyploids. Polyploid plants are currently produced sporadically in natural populations and appear to be easily generated by unreduced gametes. Most polyploid populations in the Great Basin apparently arose recently and erupted into extensive stands because of the sudden availability of large, relatively uniform domains provided by the disappearance of Pleistocene lakes.     

Theligonum cynocrambe: Developmental morphology of a peculiar rubiaceous herb

The annual Mediterranean herbTheligonum cynocrambe shows a peculiar combination of morphological characters, e.g., switch from decussate to spiral phyllotaxis with 90–100° divergence, combined with a change from interpetiolar to lateral stipules, anemophily, lack of calyx, flowers often dimerous to trimerous, corolla fused in both male and female flowers, male flowers extra-axillary, with 2–19 stamens per flower, female flowers axillary, with inferior uniovulate ovary, basilateral style and perianth, nut-like fruits with elaiosome. In male flowers the androecium emerges as an (uneven) elliptical rim with a central depression. This common girdling primordium is divided up into several stamen primordia. In male flowers with low stamen number the stamen primordia may occupy the corners alternating with the corolla lobes. There are no epipetalous androecial primordia that secondarily divide into stamens. Male flowers occasionally show a hemispherical base that may be interpreted as remnant of the inferior ovary. In female flowers a ring primordium grows into a tube on which the petal lobes arise. The perianth and style become displaced adaxially by uneven growth of the inferior ovary. The ovary is basically bilocular. The lower region of the ovary is provided with a septum that is overtopped and hidden by the single curved ovule.Theligonum is referred to theRubiaceae-Rubioideae, with theAnthospermeae andPaederieae as most closely related tribes.     

The need to re-investigate the nature of homoplastic characters: an ontogenetic case study of the 'bracteoles' in Atripliceae (Chenopodiaceae)

Background and Aims

Within Chenopodioideae, Atripliceae have been distinguished by two bracteoles enveloping the female flowers/fruits, whereas in other tribes flowers are described as ebracteolate with persistent perianth. Molecular phylogenetic hypotheses suggest ‘bracteoles’ to be homoplastic. The origin of the bracteoles was explained by successive inflorescence reductions. Flower reduction was used to explain sex determination. Therefore, floral ontogeny was studied to evaluate the nature of the bracteoles and sex determination in Atripliceae.

Methods

Inflorescences of species of Atriplex, Chenopodium, Dysphania and Spinacia oleracea were investigated using light microscopy and scanning electron microscopy.

Key Results

The main axis of the inflorescence is indeterminate with elementary dichasia as lateral units. Flowers develop centripetally, with first the formation of a perianth primordium either from a ring primordium or from five individual tepal primordia fusing post-genitally. Subsequently, five stamen primordia originate, followed by the formation of an annular ovary primordium surrounding a central single ovule. Flowers are either initially hermaphroditic remaining bisexual and/or becoming functionally unisexual at later stages, or initially unisexual. In the studied species of Atriplex, female flowers are strictly female, except in A. hortensis. In Spinacia, female and male flowers are unisexual at all developmental stages. Female flowers of Atriplex and Spinacia are protected by two accrescent fused tepal lobes, whereas the other perianth members are absent.

Conclusions

In Atriplex and Spinacia modified structures around female flowers are not bracteoles, but two opposite accrescent tepal lobes, parts of a perianth persistent on the fruit. Flowers can achieve sexuality through many different combinations; they are initially hermaphroditic, subsequently developing into bisexual or functionally unisexual flowers, with the exception of Spinacia and strictly female flowers in Atriplex, which are unisexual from the earliest developmental stages. There may be a relationship between the formation of an annular perianth primordium and flexibility in floral sex determination.     

DEVELOPMENT AND VASCULATURE OF THE FLOWERS OF LOPHOTOCARPUS CALYCINUS AND SAGITTARIA LATIFOLIA (ALISMACEAE)

The development of the bisexual flower of Lophotocarpus calycinus and of the unisexual flowers of Sagittaria latifolia has been observed. In all eases floral organs arise in acropetal succession. In L. calycinus, after initiation of the perianth, the first whorl of stamens to form consists of six stamens and is ordinarily followed by two alternating whorls of six stamens each. The very numerous carpels arc initiated spirally. In the male flower of S. latifolia the androecium develops in spiral order. A few rudimentary carpels appear near the floral apex after initiation of the stamens. There are no staminodia. The female flower has a similar developmental pattern to that of Lophotocarpus except that a prominent residual floral apex is left bare of carpels. The vascular system in all flowers is semiopen, with vascular bundles passing to the floral organs in a pattern unrelated to the relative positions of those organs. The androecia of these two taxa are similar to those of some Butomaceae and relationships based on ontogeny and morphology are suggested. The gynoecia are meristically less specialized but morphologically more specialized than the gynoecia of Butomaceae.     

ELEMENTAL DISTRIBUTION IN SEEDS OF THE HALOPHYTES SALICORNIA PACIFICA VAR. UTAHENSIS AND ATRIPLEX CANESCENS

Little information is available on the distribution of ions in seeds of halophytes. Seeds of two halophytes, Salicornia pacifica var. utahensis (Tidestrom) Munz, a desert salt playa type, and Atriplex canescens (Pursh) Nutt., a desert shrub, were analyzed by energy dispersive X-ray microanalysis. The relative ion concentration in three regions, the seed coat, endosperm, and embryo, were determined. The total relative concentration of elements was higher in seeds of S. pacifica var. utahensis as compared to A. canescens. The seed coats of S. pacifica var. utahensis contained the highest counts of sodium, chlorine, potassium, and calcium, whereas the embryo and endorsperm were both high in phosophorus. In A. canescens, sodium and chlorine were very low in all three tissues. The embryo contained the major amount of phosphorus, although potassium was high in both the seed coat and the embryo. These results support the concept of ion compartmentalization in the seeds of these two halophytes.     

Floral ontogeny and systematic position of the Didiereaceae

Floral ontogenetical data from all four genera of the Didiereaceae (s.str.) are presented for the first time. All Didiereaceae s.str. are dioecious, having unisexual flowers with organ rudiments of the opposite sex. Two median bracts followed by a tetramerous perianth (two alternating dimerous ``whorls'), a slightly complex androecium with 6–12 stamens in a single row (on a common ring primordium), four of which mostly alternating with the perianth members, and one basal ovule connecting three free septa at their very base are flower characters in Didiereaceae, supporting phylogenetic analyses based on nucleotide sequence data. Closest relatives are the (formerly) portulacaceous genera Portulacaria (5 stamens alternating with the perianth), Ceraria (5 stamens alternating with the perianth), and Calyptrotheca (many stamens), all with pentamerous perianths, from which the tetramerous perianth in Didiereaceae can be derived. Applequist and Wallace (2003) included these three genera in an expanded family Didiereaceae (with three subfamilies).     

I. LIFE HISTORY FEATURES OF THREE SEXUAL MORPHS OF ATRIPLEX CANESCENS (CHENOPODIACEAE) CLONES GROWN IN A COMMON GARDEN

Reproductive and growth parameters of Atriplex canescens were examined in a common garden study. Cloned ramets of male, female, and hermaphrodite individuals from two natural populations were planted in irrigated and nonirrigated portions of the garden. Sexual differences in growth and flowering schedules suggest tradeoffs in resource allocation between growth and reproduction. Males flowered with the greatest frequency and intensity while producing the smallest growth parameters. Females had the largest measures of vegetative growth, but flowered with the least frequency and intensity. Hermaphrodites appear to have a biology distinct from males and females, being more like females in growth and more like males in reproduction.     

INFERIOR OVARY AND GENERIC AFFINITIES OF GARRYA

Characters of the inflorescence and flower distinguish 2 sections in Garrya. Female flowers of sect. Garrya bear 2 small epigynous appendages, usually considered a rudimentary perianth. In sect. Fadyenia, female flowers are nude, but occasionally 2 more or less foliaceous bracts are partially adnate to the ovary, sometimes simulating the appearance of appendages in sect. Garrya. Authors who have observed this infer that the adnate bracts are homologous to epigynous appendages in sect. Garrya and that the ovary, therefore, cannot be considered inferior. This inference, if valid, would weigh against a close relationship between Garrya and Cornaceae. Clearing and sectioning show, however, that the vascular pattern in flowers of sect. Garrya is similar to the pattern in many Cornaceae. Perianth bundles are united with ventral carpellaries for most of their length, whereas bundles of the adnate bracts in sect. Fadyenia are associated with dorsal carpellary strands; therefore, the 2 kinds of appendages are not homologous. In gynoecial characters Garrya most closely resembles Griselinia and, to a lesser extent, A ucuba. These 3 genera probably had a common origin within the Cornaceae.     

THE ONTOGENY OF THE INFLORESCENCE AND FLOWER OF LIQUIDAMBAR STYRACIFLUA L. (HAMAMELIDACEAE)

A developmental study of the inflorescence of Liquidambar styraciflua L. was conducted to clarify morphological discrepancies reported in the literature. Salient features of development are: 1) the inflorescence apex results from the conversion of a terminal, vegetative apex; 2) partial inflorescence apices arise as ellipsoid structures in axils of leaves, bracts, or transitional phyllomes; 3) development of male heads is acropetal whereas female heads differentiate basipetally; 4) the partial inflorescence apex becomes segmented into several distinct subunits indicating an axillary branch system of the third order; 5) distinct individual floral primordia are initiated on the subunits; 6) a complete absence of perianth development; 7) inception of carpel primordia in flowers of lower male heads as well as female heads, but a failure of the gynoecium to develop beyond an incipient stage in male heads; and 8) development of sterile structures around the base of the styles of only female flowers near the time of anthesis. Carpellary characteristics of the sterile structures are described, their morphological nature is discussed, and the phylogenetic position of Liquidambar is evaluated.     

Auxin and physical constraint exerted by the perianth promote androgynophore bending in Passiflora mucronata L. (Passifloraceae)

The androgynophore column, a distinctive floral feature in passion flowers, is strongly crooked or bent in many Passiflora species pollinated by bats. This is a floral feature that facilitates the adaptation to bat pollination. Crooking or bending of plant organs are generally caused by environmental stimulus (e.g. mechanical barriers) and might involve the differential distribution of auxin. Our aim was to study the role of the perianth organs and the effect of auxin in bending of the androgynophore of the bat‐pollinated species Passiflora mucronata. Morpho‐anatomical characterisation of the androgynophore, including measurements of curvature angles and cell sizes both at the dorsal (convex) and ventral (concave) sides of the androgynophore, was performed on control flowers, flowers from which perianth organs were partially removed and flowers treated either with auxin (2,4‐dichlorophenoxyacetic acid; 2,4‐D) or with an inhibitor of auxin polar transport (naphthylphthalamic acid; NPA). Asymmetric growth of the androgynophore column, leading to bending, occurs at a late stage of flower development. Removing the physical constraint exerted by perianth organs or treatment with NPA significantly reduced androgynophore bending. Additionally, the androgynophores of plants treated with 2,4‐D were more curved when compared to controls. There was a larger cellular expansion at the dorsal side of the androgynophores of plants treated with 2,4‐D and in both sides of the androgynophores of plants treated with NPA. This study suggests that the physical constraint exerted by perianth and auxin redistribution promotes androgynophore bending in P. mucronata and might be related to the evolution of chiropterophily in the genus Passiflora.     

Taxonomic position and distribution of Atriplex lapponica (Chenopodiaceae)

The arctic, halophytic species Atriplex lapponica Pojark has flowers of two kinds: perfect ones surrounded by a pentamerous perianth and pistillate flowers enclosed in bracteoles. Thus, A. lapponica is closely related to the species of sect. Dichospermum Dumort, not to species of sect. Teutliopsis Dumort. as generally believed.     

Floral development and evolution of capitulum structure in Anacyclus (Anthemideae,Asteraceae)

Background and Aims

Most of the diversity in the pseudanthia of Asteraceae is based on the differential symmetry and sexuality of its flowers. In Anacyclus, where there are (1) homogamous capitula, with bisexual, mainly actinomorphic and pentamerous flowers; and (2) heterogamous capitula, with peripheral zygomorphic, trimerous and long-/short-rayed female flowers, the floral ontogeny was investigated to infer their origin.

Methods

Floral morphology and ontogeny were studied using scanning electron microscope and light microscope techniques

Key Results

Disc flowers, subtended by paleae, initiate acropetally. Perianth and androecium initiation is unidirectional/simultaneous. Late zygomorphy occurs by enlargement of the adaxial perianth lobes. In contrast, ray flowers, subtended by involucral bracts, initiate after the proximal disc buds, breaking the inflorescence acropetal pattern. Early zygomorphy is manifested through the fusion of the lateral and abaxial perianth lobes and the arrest of the adaxials. We report atypical phenotypes with peripheral ‘trumpet’ flowers from natural populations. The peripheral ‘trumpet’ buds initiate after disc flowers, but maintain an actinomorphic perianth. All phenotypes are compared and interpreted in the context of alternative scenarios for the origin of the capitulum and the perianth identity.

Conclusions

Homogamous inflorescences display a uniform floral morphology and development, whereas the peripheral buds in heterogamous capitula display remarkable plasticity. Disc and ray flowers follow different floral developmental pathways. Peripheral zygomorphic flowers initiate after the proximal actinomorphic disc flowers, behaving as lateral independent units of the pseudanthial disc from inception. The perianth and the androecium are the most variable whorls across the different types of flowers, but their changes are not correlated. Lack of homology between hypanthial appendages and a calyx, and the perianth double-sided structure are discussed for Anacyclus together with potential causes of its ray flower plasticity.     

A new species ofThottea (Aristolochiaceae) from India

Thottea ponmudiana sp. nova from Kerala (India) can readily be distinguished from its closest allyTh. siliquosa and all the other known species of the genus by its yellow flowers with purple eyes, deeply lobed perianth with strongly reflexed margins, uniseriate stamens united in three bundles and strongly 4-angled, green, glabrescent fruits.     

MORPHOLOGICAL STUDIES OF THE NYMPHAEACEAE. XI. THE FLORAL BIOLOGY OF NELUMBO PENTAPETALA

The floral biology of Nelumbo pentapetala (Walter) Fernald, the American lotus, native to Texas, was investigated. Anthesis occurs over three consecutive days with flowers opening each morning and closing around noon. First-day flowers are protogynous with the perianth parts partially expanded so that pollen-covered insects which are attracted by floral color and the intense “fruity” odor (diffused with the aid of increased floral temperature) are directed on to the flattened receptacle (= carpellary receptacle) from which the receptive stigmas protrude, thus accomplishing pollination. During the second morning anther dehiscence begins and insects which visit and forage within the flower become covered with pollen and typically crawl over the still receptive stigmas achieving “facilitated” self-pollination (indirect autogamy). By mid-morning of the second day the stigmas dry and become non-receptive to pollen. During the third day of anthesis perianth and staminal parts quickly abscise and over the period of a few weeks the receptacle and enclosed fruits mature. In most populations studied, Hymenoptera (e.g., Lusioglossum spp., and Apis mellifera) were the most abundant and effective pollinators. In some populations, however, Coleoptera (e.g., Chauliognathus) were also numerous and effective pollinators. It is suggested that the overall floral structure (e.g., large numbers of stamens, masses of pollen, staminal appendages) are adaptations which facilitate the pollination of Nelumbo by beetles.     

INVESTIGATIONS OF ANGIOSPERMS FROM THE EOCENE OF NORTH AMERICA: A CATKIN WITH JUGLANDACEOUS AFFINITIES

Three specimens of one type of fossil catkin from the Middle Eocene of Tennessee are excellently preserved and have been investigated morphologically. The flowers on these catkins are subtended by elongate, three-lobed bracts, are exclusively staminate, and have three conspicuous, obovate, perianth parts that bear large peltate scales. The stamens are well preserved and contain triporate pollen grains that are equivalent to the dispersed pollen genus Momipites. Floral morphology, cuticular features, and pollen indicate close affinities with the extant genera Engelhardia, Oreomunnea, and Alfaroa of the Juglandaceae; but because the fossil catkins are distinct and are a dispersed plant organ, they are placed in a new form genus: Eokachyra. These fossil flowers represent a rare opportunity to correlate the micro- and macrofossil record and to compare the relative rates of evolution of these features. The fossil catkins also demonstrate that much structural information may be gained from the study of fossil angiosperm flowers. The similarities between the staminate flowers of the fossil catkins and the staminate flowers of Engelhardia, Oreomunnea, and Alfaroa confirm the idea that this complex has had a long evolutionary history and suggest that the pollination system of certain extant genera was well developed during Middle Eocene times.