A partial inflorescence and two flowers from the Middle Eocene Princeton Chert,
British Columbia, Canada, digitally reconstructed from serial sections using the
program AMIRA 3.1.1. The raceme (left) represents an immature apical portion of
the inflorescence, 2.9 mm long, with bracts (white) and stamens (green) visible.
Fossil flowers are only 0.8 mm in diameter, making the use of three-dimensional
reconstructions extremely helpful in visualizing the whole flowers. Flowers have
a subtending bract (white), no perianth, five stamens (yellow) and four carpels
(green). Anatomy, morphology and phylogenetic analysis indicate these fossils
are most similar to Saururus (lizard
Flower of Trigonidium egertonianum, an orchid in the subtribe Maxillariinae.
Flowers of Trigonidium are pollinated by pseudocopulation by meliponine
bees attracted to the bluish petal apices; the bees attempt to copulate with the
flowers and become trapped in the funnel-shaped flowers. On the basis of molecular
data, Trigonidium was found to be embedded in the large polyphyletic
Silene latifolia, or white campion (formerly Melandrium album), is a well-recognized historical model of plant dioecy and heteromorphic sex chromosomes. Its large genome of 3012 Mbp is organized in 12 pairs of chromosomes, one of these pairs being sex chromosomes: XY in males and XX in females. The metaphase sex chromosomes can be easily distinguished from autosomes because the Y chromosome is the largest at c. 570 Mbp, and the X chromosome is second largest, at c. 400 Mbp. The Y chromosome has at least three genic regions responsible for the development of male (staminate) flowers; one of these Y-linked genic regions corresponds to suppression of carpel development in male flowers. The absence of the Y chromosome leads to female floral development (exclusive carpel formation). This fluorescence image shows the metaphase chromosomes from a male individual with the X and Y chromosomes indicated. Chromosomes were counterstained with DAPI (diamino phenylindole, here in red) and tagged with two fluorescent DNA probes-X-43.1 subtelomeric repeat (green) and (CAT)10 microsatellite (yellow).
Light micrograph of the vein pattern of a New World endemic, Flaveria trinervia (Spreng.) C. Mohr., a pantropical weedy C4 species. Flaveria is of special interest because of its diversity in photosynthetic types; it has species classified as having C3, C4, or intermediate photosynthesis. This clearing of a mature leaf of F. trinervia, viewed with differential interference contrast optics, shows a reticulate pattern with high vein density and distinctive bundle sheath tissue. These two features are part of a critical suite of anatomical characteristics (Kranz anatomy) that has evolved independently many times to support C4 biochemical functioning; many variations of Kranz anatomy exist, especially in the eudicots.
Tristerix penduliflorus (Loranthaceae) is a bird-pollinated mistletoe
that occurs in dry, high elevation (3700 m) habitats from southern Peru to Bolivia.
This plant, parasitic on Schinus (Anacardiaceae), was photographed near
Maras, Departamento Cuzco, in southern Peru (scale: 3.83× unopened flower
buds are typically 3.7 cm long). Although the flower color pattern suggests affinity
with other Peruvian species, molecular data indicate that T. penduliflorus
is related to three Tristerix species with more southern distributions.
One of these southern species from central Chile, T. aphyllus, appears
to have arisen in sympatry from T. corymbosus, an event accompanied by
a host switch driven by the behavior of a seeddispersing bird.
Tension tissue in transverse hand section of internode 7 from unfixed wild-type
alfalfa (Medicago sativa), shown for the first time in an herbaceous
perennial using zinc chloro-iodide staining and differential interference contrast
to increase resolution of unstained cells (c. 100X). Tension tissue in angiosperms,
associated with mechanical strengthening of stems and branches to offset leaning
or other mechanical challenges, is sometimes correlated with the presence of
gelatinous fibers and/or reduced lignin content. The inner layers of the gelatinous
fibers stained dark red to purple, and the lignified outer cell walls stained
orange to yellow. Reaction phloem fibers were also identified above the reaction
xylem. The tension tissue was discovered not only in the wild type, but also
to a greater extent in alfalfa line pC3H-I with c. 64% less lignin. In addition,
tension tissue alters cell wall properties to help provide sufficient mechanical
support in the lignin downregulated line. Tension wood, however, is often viewed
as deleterious in pulp/paper and lumber manufacture; this study raises the possibility
of its increased formation in biotechnologically modified lignin-reduced woody
Light micrograph of a young leaf of lace plant at the perforation stage of
leaf development. The blue cells within three perforation sites that are undergoing
programmed cell death (PCD) are stained specifically for cell wall pectins by
alcian blue as a result of cuticle degradation. Adjacent living cells with intact
cuticle are not stained. The resculpting of a simple leaf blade is a unique
use of developmental PCD, known only for this species and for a handful of genera
in the aroid family. The accessibility and predictability of perforation formation
in lace plant leaves and the ability to propagate lace plant in sterile conditions
make the lace plant an attractive model for the study of developmental PCD in
plants. Scale bar = 100
The tropical montane basidiolichen Dictyonema glabratum in Volcan Tenorio
National Park in Costa Rica (c. 3X actual size). The lichen symbiosis is one of
the predominant life forms in Fungi, but Basidiomycota have very few lichenized
species (e.g., in the genera Dictyonema, Lichenomphalia, and
Multiclavula), and most of them are rare and found in specific habitats.
Dictyonema glabratum is the most abundant and widespread species and
often found in large quantities on open road banks, but it is also epiphytic on
shrubs and trees. Discoveries of novel basidiolichens are rare, but a new species
of Multiclavula with a unique, previously unknown basidiocarp morphology
was discovered during the NSF-funded TICOLICHEN biodiversity inventory in Costa
The vegetative anatomy of root holoparasitic plants is difficult to interpret
because of its dramatic morphological reduction. This root holoparasitic plant,
Hydnora africana Thunb., parasitizing Euphorbia mauritanica
L. (background) in the Richtersveld of South Africa, only emerges from the soil
to flower. After the fleshy petals open, the flower emits an odor of rotting
meat to attract its pollinators, carrion flies and beetles. In anatomical investigations,
the vegetative body of Hydnora triceps Drège & Meyer was
revealed to be a rhizome with an unusual modified root-cap-like structure and
xylem characteristic of its Piperalean stock.
Light micrographs of median longitudinal sections of root apical meristems
(RAMs) from basal angiosperms, monocots, and eudicots are pictured, left to
right: top, Magnolia grandiflora, Cabomba caroliniana, and Ranunculus
muricatus; bottom, Clivia miniata, Commelina communis, and
Quercus rubra. This project, to characterize the arrangement of patterns
of cells in the organization of angiosperm RAMs, was conceived by Heimsch in
the early 1950s; the specimens in this montage of root tips were produced from
1956 until 2003 and were photographed with brightfield illumination on a Zeiss
Axiophot microscope (University of Waterloo).
One of the fundamental characteristics of plants is their polar organization
and polar growth. An auxin gradient has been implicated in directing all polar
patterns of development and differentiation. Auxin effl ux carriers, PINs, present
only in specifi c cell membranes, drive polar auxin transport and the PID protein
kinase in Arabidopsis regulates transport by targeting PIN transporters.
If this gene plays the same role in all plant species, it must be among the
most important genes that control morphological diversity. The PsPK2
gene, the PID homolog in pea, is expressed in all growing parts of pea
and is positively regulated by auxin, gibberellin, and cytokinin. To compare
regulatory characteristics of PsPK2 and PID, we constructed a
reporter gene and transformed Arabidopsis with it. GUS activity is illustrated
in transgenic PsPK2::GUS (upper 3 rows) and DR5::GUS (lower 3
rows) Arabidopsis seedlings in response to treatment with water (control)
and four auxins: 4-chloro-indole acetic acid (4-Cl-IAA), indole-3- acetic acid
(IAA), indole-3-butyric acid (IBA), indole-3- acetic acid methyl ester (MeIAA),
Variation in hip (fruit) morphology in rose species (Rosa spp., Rosaceae).
In traditional Rosa classifications, this morphological variation is
utilized for sub-division into subgenera, sections, and subsections. However,
the genus Rosa has a complex evolutionary history that is not always
adequately reflected in morphological characters. As a result, morphology can
be an unreliable indicator of phylogenetic relationships in Rosa.
Light micrograph of a cucumber root tip releasing border cells after immersion
in water. Recent concern about global warming and the underlying anthropogenic
increase in atmospheric CO2 has led to intense interest in carbon
cycles. One component of the carbon cycle is soil sequestration of carbon, which
is ecologically important. Much of the underground cycling of carbon occurs
in rhizospheres, small layers of soil surrounding and influenced by the roots
of higher plants. Throughout its lifetime, a plant root releases organic carbon
to its rhizosphere. Carbon-containing exudates have been found to be particularly
abundant at root tips and at points of initiation of branch roots. The root
tips, including root caps, meristems, and elongation zones, are particularly
active in secreting sugars, organic acids, and specialized compounds such as
phytosiderophores. Mucilage, containing high molecular weight polysaccharides
(particularly polyuronic acids), is produced copiously by root caps and cortical
cells. These carbon sources sustain the rich microflora of the rhizosphere.
Another source of carbon is provided by border cells, a subset of peripheral
root cap cells. These cells are formed as part of the root cap and released
from the exterior of the cap to live freely in the soil for a time. Border cells
are known to exert antibiotic effects, protecting plants from certain pathogenic
microbial infections, and stimulating the growth of other microbes. While examining
the importance of border cell release to carbon cycling in soils, we made the
unexpected discovery that the number of cells released is strongly dependent
on the developmental stage of the root. In four species that were examined,
young, short seedling roots released thousands, while roots longer than 4 cm
released only tens to hundreds of border cells. This developmental program is
hypothesized to protect the plant during the critical period of radicle penetration
of the soil following germination and during seedling establishment.
Marattia howeana (W.R.B.Oliv.) P.S.Green, a rare endemic to Lord Howe
Island with only a few known remaining populations. Several marattioid fern
species, including M. howeana and the Hawaiian endemic M. douglasii
(C. Presl) Baker, are seriously threatened by introduced feral pigs who favor
the sweet fleshy rhizome as a food source. The fully fused synangia (fused sporangia,
ca. 3–5 mm in length), characteristic of Marattia s.l., are captured
in this photo just at the stage of dehiscence. This photo was taken from live
material grown at Humboldt State University, Arcata, California, where new methods
for efficient asexual propagation of marattioid ferns are currently under development.
For further details, see Murdock: Phylogeny of marattioid ferns (Marattiaceae):
inferring a root in the absence of a closely related outgroup, American
Journal of Botany, Volume 95, Issue 5, pages 626-641, http://www.amjbot.org/cgi/content/short/95/5/626.
Of the estimated 1.5 million species of fungi, only 5% are presently known
to science, but even this small fraction includes a bewildering variety of forms
and ecological types. Recent Tree of Life studies have begun to clarify the
complex relationships observed in most fungal groups, and new discoveries aid
in this effort. A new species of Marchandiomyces, discovered recently
in Australia by Guy Marson and described in this issue, is helping to shed light
on the remarkable nutritional diversity of the basidiomycete order Corticiales,
which includes saprophytes, plant and fungal pathogens, lichen-forming fungi,
and now leaf-inhabiting (foliicolous) species. The new species produces small,
coral bulbils (inset) on the dead leaves of screw pines (Pandanus oblatus).
These bulbils, which probably function as resting or dispersal structures, resemble
apothecia of the ascomycete genus Orbilia, which Marson was collecting
at the time. This first Marchandiomyces species described from Australia
is unusual not only in appearance, but also in ecology. A new molecular phylogeny
of the Corticiales, including M. marsonii, makes clear that Marchandiomyces
species contribute significantly to the nutritional diversity of the order.
Menispermites cordatus, a new fossil leaf species from the middle–late
Paleocene (ca. 60-58 Mya) of the Cerrejón paleoflora, northern Colombia.
Leaf morphology and venation patterns are remarkably similar to those of the
modern lianas of Menispermaceae. The presence of climbing plants and tall canopy
trees in the Cerrejón Paleocene forest suggests that multistratification
of Neotropical rain forests is an ancient feature.