Field botanists often have clever ways to identify species that are difficult to distinguish from each other without a microscope or reference to herbarium specimens. Usually the scientific basis or mechanism of such a
Buds of yellow buckeye (Aesculus flava, Sapindaceae) showing expanding
new leaves under an open canopy in early spring (ca. 15 March) Great Smoky Mountains
National Park, Tennessee, USA. Yellow buckeye is the earliest tree species to
produce a flush of new leaves in the southern Appalachians. Early leaf emergence
increases light capture before canopy closure and may provide a substantial
copyright: Omar R. Lopez, BSA license: http://images.botany.org/index.html#license
Leaf nectary of Prockia crucis P. Browne ex. L. (Salicaceae) with
a drop of sucrose-rich, high-energy nectar, which may be attractive to visitors.
Some species of aggressive ants get nectar from extrafloral nectaries, meanwhile
protecting the plant's leaves. This interaction may be an important strategy
to enhance the adaptive success of the species. These highly structured nectaries
are similar to the salicoids teeth of the Populus and Salix
species, lending strong support to the phylogenetic proximity of these clades.
For further detail: see Thadeo et al.
copyright: Renata M. S. A. Meira, BSA license: http://images.botany.org/index.html#license
Stem cross section of Pereskia guamacho, a member of the eight-species cactus lineage hypothesized to be sister to the remaining 1800 or so species of Cactaceae. Pereskia guamacho is a leafy, dry-forest tree lacking many anatomical traits, such as stem succulence, mucilage cells, delayed periderm, and stem stomata, that are highly conserved in most other cacti. Rather than the evolution of a single
Contrary to conventional wisdom, the life cycle of Arabidopsis thaliana does not consist of a vegetative rosette that is the source of carbon production followed by a reproductive inflorescence that is a carbon sink. Earley et al. show instead that the inflorescence contributes much of the lifetime carbon gain, from 36 to 93%, depending on the genotype, and with much less water lost per unit carbon gained compared to the rosette. They suggest that the switch from rosette to inflorescence is an ontogenetic niche shift that allows the plant to successively exploit the warm air at the soil boundary during the cool season and escape into the freely moving air in warm season. This shift also results in a more water-use efficient plant during the warm season.
Stanleya pinnata (prince's plume) can hyperaccumulate the toxic element selenium (Se) up to 0.5% of its dry mass in its natural habitat in the western United States. In a 2-year manipulative field experiment to test whether S. pinnata uses Se as an elemental defense against one of its native mammalian herbivores, the blacktailed prairie dog (Cynomys ludovicianus), plants with high Se concentrations had higher survival rates and less herbivory than low-Se counterparts when planted in black-tailed prairie dog towns. These results give better insight into the evolution of plant Se hyperaccumulation, suggesting a role for herbivory as a possible selection pressure. From an applied perspective, plants that accumulate Se may be cultivated for phytoremediation or as fortified foods, and this study helps assess the associated risk of Se moving up the food chain.
An unidentified twining liana from French Guiana. Lianas are often difficult to identify because the leaves and flowers may be high in the canopy. Lianas are an important component of the forest where they may represent 10 to 45% of woody stems in some tropical forests, and comprise as much as 40% of the diversity of woody species. Rooted in the soil, climbing plants have evolved a large diversity of strategies to ascend supports and reach light in the canopy. Some species may twine around supports (see videos in the online Supplemental Data) and form a strikingly uniform helix, which will squeeze the host and provide stability under gravitational loads; others use sensitive or sticky organs to cling onto the surrounding vegetation, or hooks to anchor to bark or small branches. For lianas, anything and everything in relation to host plants can be used for mechanical stability with little expenditure in structural support. This fascinating aspect of climbing plants has long attracted the attention of botanists since Darwin's seminal work
copyright: BSA, S. Isnard license: http://images.botany.org/index.html#license
Numerous complex mathematical theories have been proposed to explain why annual growth rates of plants scale as the 3/4 power of total body mass, why total leaf mass per plant scales as the square of trunk diameter, and why a host of other widely reported ecological phenomena occur. In this issue, Hammond and Niklas unveil a new computer model, called SERA (for spatially explicit reiterative algorithm), which accurately predicts these and many other scaling relationships as plants are forced to conform mathematically to a few very simple physical principles while they compete for light and space. In each SERA simulation, tree canopies are depicted as thinshelled hemispheres and trunks are modeled as simple, untapered cylinders that increase in girth as simulated plants age. A hypothetical landscape is randomly seeded with a specified number of propagules and monitored during every growing season to assess biomass- and age-dependent allometric relationships. A graphic module allows a population or community to be observed at any stage in its growth as old plants die and new ones propagate. In this image, the observer is standing at ground level and looking up into a forest composed of a single species mathematically modeled to mimic the allometry of a population of Abies alba.
Cuscuta (dodders) species are obligate parasitic plants with stems that resemble yellow-orange spaghetti. Their seedlings can detect and select among potential hosts using volatile chemical cues. Dodders can transfer viruses, mycoplasmas, and macromolecules from one host to another, and they are involved in the translocation of mRNA from their hosts and in horizontal gene transfer spanning deep phylogenetic distances. Similar to other parasitic plants, Cuscuta spp. have been described as keystone species and as
Longitudinal section of developing caryopsis of maize ancestor, teosinte (Zea mays ssp. parviglumis, caryopsis diameter cca. 3 mm). Teosinte plants differ significantly from domesticated maize Zea mays ssp. mays. Teosinte plants have many lateral branches with terminal male inflorescences, which closely resemble maize tassels, and small female inflorescences or
copyright: BSA, Ales Kladnik license: http://images.botany.org/index.html#license
Reproductive stem of Monotropsis odorata (sweet pine sap; Ericaceae), a nonphotosynthetic plant endemic to the southeastern United States. As a myco-heterotroph, M. odorata obtains carbon resources from associated mycorrhizal fungi and has a highly reduced vegetative morphology consisting of an underground root mass that produces one to many diminutive reproductive stems (3.5
copyright: BSA, Matthew R. Klooster license: http://images.botany.org/index.html#license
The arid habitat of the Antelope Valley California Poppy Preserve, USA, appears dry and lifeless for much of the year, but following the rainy season it bursts with the brilliant colors of the spring wildflower bloom. Many insects can be seen flying about pollinating flowers as they collect nectar and pollen. In this photo, a hover fly can be seen collecting pollen from a Phacelia (Hydrophyllaceae) flower. The fly has a short thick vacuum-like mouth, which it uses to suck up pollen from the flower anther. Although hover flies eat much of the pollen they collect, they also provide a valuable service to flowers by transferring pollen from one flower to another.
Scientific Description/Explanation: The genus Garrya
Dougl. ex Lindl. [See "Terms From Scientific Description,"
below, for explanations of terms in italics] (Garryaceae) contains
15 species of winter-blooming, wind-pollinated, dioecious evergreen
trees and shrubs distributed in North America (including Mexico), Central
America, and the Caribbean Islands. The genus Garrya is found only
in the New World, but is closely related to the genus Aucuba, which
is native to China and Japan. The genus Garrya is thought to represent
a relatively recent introduction to the New World, which probably migrated
from Asia over a high-latitude land-bridge sometime during the last twenty
million years. Garrya fremontii is a widespread species that occurs
from central California to Washington State. It is most abundant at middle
and high elevations (1000-3000 meters) in parts of the Sierra Nevada Mountains,
the Pacific Coast Ranges, and the Cascade Range. It occupies a diversity
of habitats, from chaparral and oak woodland to coniferous forests. The
plant in the photograph is part of a population of Garrya fremontii
growing on Doe Mill Ridge in Butte County, California, about 15 kilometers
north-northeast of the town of Chico. These plants are part of a dense chaparral
community composed mainly of species of Arctostaphylos (manzanita)
and Ceanothus. This community is strongly fire regulated, with
fires occurring about every seven to ten years. Garrya fremontii,
along with many other members of this chaparral community, survives fire
by re-sprouting from a buried root-crown, or lignotuber. It also regenerates
from seeds deposited in the soil seed-bank. Garrya fremontii is
part of a complex of species from western North America, within which the
species are very difficult to differentiate. Garrya fremontii intergrades
morphologically with Garrya flavescens in the coast ranges of California,
which may indicate that these two taxa are not distinct. In addition, preliminary
results using DNA sequence data (see URL below) suggest that there
is very little genetic variation among species of Garrya in California.
Like all species in the genus, Garrya fremontii flowers during
the late winter, long before most plants have begun their growing season.
The flowers are born in pendulous inflorescences, as shown in the
image, and have a unique, highly reduced structure. In female inflorescences
the flowers are arranged in successive groups that are each partially surrounded
by a bract. In the photograph, these bracts are obvious as the
greenish, triangular flaps that cover the bases of the silky, developing
ovaries. Opposite bracts sometimes fuse, forming a cup that surrounds
multiple groups of flowers. Individual female flowers lack almost all vestiges
of a corolla or calyx, although minute remnants of these
structures are sometimes present near the base of the styles. The
presence of these perianth remnants is usually taken as evidence
that the ovaries of Garrya fremontii are inferior. The
ovaries of all Garrya species are composed of two carpels,
and thus produce two seeds. The styles of Garrya fremontii are
characteristically elongated and thin, often recurving toward the inflorescence
axis, which gives the appearance of a "handle-bar mustache." This
character is clearly visible in the image, although some of the styles have
dried up and broken off, as the inflorescence in the image is several weeks
old and past the fertilization stage. Male inflorescences are not shown
in the image, but male plants were present in the vicinity of the pictured
plant. Male inflorescences are also morphologically reduced, and specialized
for wind pollination. These adaptations include a special chamber formed
from the distally fused perianth members that is thought to aid
in preventing desiccation of the pollen. The male inflorescence is also
less rigid than the female inflorescence, which enables it to flex with
the wind currents. Most species of Garrya flower well before the
time when potential pollinators are active, sometimes while snow is still
on the ground, so scientists have inferred that they are wind pollinated.
The fruits of Garrya fremontii mature in the fall, and are dark
blue in color. It is not certain what the primary dispersal agent of this
plant may be, but species of Neotoma (wood rats) are known to collect
them. Overall, Garrya fremontii, and the genus Garrya
in general, present an intriguing combination of highly derived
morphological traits, unusual ecology, and potentially complex genealogical
and geographical patterns going back to the Old World. Garrya also
takes readily to cultivation, and several species and hybrids are popular
landscape plants in the Western United States. TERMS FROM THE EXPLANATION
<font color="#666666">Garrya</font> - The scientific name of any
organism should always be underlined or printed in italics. The scientific
name of an organism always has two parts, the genus name (Garrya,
for instance), and the species name (fremontii, for instance).
Because of the parts of speech corresponding to these two words, and convention,
the first is always capitalized, while the latter is never capitalized.
<font color="#666666">Dougl. ex Lindl</font>- In plant
taxonomic treatments, papers, floras, labels, etc., the name of a plant
taxon is often given along with the name of the authority for that taxon
(the author of the taxon name). In the case of the genus Garrya,
the authority is Lindley, who was the first to validly publish (sanction)
the name Garrya, which had been proposed, but not validly published,
<font color="#666666">Dioecious</font> - Most plants have bisexual
flowers, with male and female parts combined within the same structure.
However, some taxa have the male and female parts separated into different
flowers. If both female and male flowers occur on the same plant, then the
species is known as monoecious. If the flowers are born on separate plants,
analogous to the two-sex system of many animals, then the plant is known
<font color="#666666">DNA sequence</font> - DNA (Deoxyribonucleic
acid) is the information-carrying molecule of living things. DNA, which
encodes information for building proteins, is the basis for almost all of
the characteristics of a given organism, as expressed during development.
Scientists use DNA to gain insight into the history of life on earth, and
the dynamics of living systems. This is possible because of the unique hereditary
role of DNA, which accumulates errors in living organisms, some of which
are passed on to subsequent generations. DNA can be extracted from living
organisms and its code, or sequence, can be read using specialized techniques.
This information may be used in a statistical fashion to infer the genealogy
of a group of organisms, such as a genus or species of plant.
<font color="#666666">Inflorescence</font> - The reproductive part
of a plant, including all flowers and the stems on which they are born,
is called an inflorescence. There is considerable diversity in
inflorescence structure among flowering plants. A daisy "flower,"
for instance, is really an inflorescence containing several hundred individual
<font color="#666666">Bract, carpel, ovary, corolla, calyx, perianth,
style</font> - Most flowers are composed of four "whorls"
of parts. (1) The female parts, or carpels, which each have an
ovary as well as a stigma (the receptive surface for pollen)
that is born on the end of a style. (2) The male parts, or stamens,
which are made up of pollen-bearing anthers on the end of filaments. (3)
The petals, which together are known as the corolla. (4) The sepals,
which are typically green and collectively called the calyx. The
calyx and corolla are together known as the perianth. All of these
flower parts are attached to a receptacle, which is often born on the end
of a stalk called the pedicel. This pedicel is often subtended by (found
immediately above) a leaf-like organ called a bract. All of the
amazing and beautiful diversity of flower morphology is simply variation
on this theme of four whorls and subtending elements.
<font color="#666666">Inferior</font> - When the corolla and calyx
become fused to the walls of the carpels so that the stamens, anthers, and
stigmas appear anatomically above the ovary, rather than below it, then
the ovaries of that flower are termed inferior. Normal ovaries
are termed superior. An apple, for example, is derived from a fertilized
flower with inferior ovaries. The perianth, stamens, and styles are often
visible in the depression on the distal end of the apple (opposite the stem,
<font color="#666666">Distally</font> - In anatomical terms, an
organ that is far from a point of reference is distal, while an
organ that is near is proximal. Your hand, for instance, is on the distal
end of your arm. These terms are used universally in discussions of both
animal and plant anatomy.
<font color="#666666">Derived</font> - Genealogies of organisms
are also known as phylogenies. Humans, apes, and monkeys, for instance,
are all related, and the specific genealogical relationships between them,
as inferred from morphological traits or DNA sequence variation, can be
expressed as a branching, tree-like phylogeny, in which the earliest-branching
lineages (those appearing lowest on the tree) are considered as ancestral,
and the most recent, latest branching lineages are considered as derived.
Bremer, B., Bremer, K., Heidari, N., Erixon, P., Olmstead, R.G., Anderberg,
A.A., Källersjö, M., & Barkhordarian, E. 2002. Phylogenetics
of asterids based on 3 coding and 3 non-coding chloroplast DNA markers and
the utility of non-coding DNA at higher taxonomic levels. Molecular
Phylogenetics and Evolution 24: 274-301.
Dahling, G.V. 1978. Systematics and evolution of Garrya. Contributions
from the Gray Herbarium of Harvard University 209: 1-104.
Eyde, R.H. 1964. Inferior ovary and generic affinities of Garrya.
American Journal of Botany 51: 1083-1092.
Graham, A. 1999. The tertiary history of the northern temperate element
in the northern Latin American biota. American Journal of Botany 86:
Hileman, L.C., Vasey, M.C., & Parker, V.T. 2001. Phylogeny and biogeography
of the Arbutoideae (Ericaceae): implications for the Madrean-Tethyan hypothesis.
Systematic Botany 26: 131-143.
Liston, A. 2003. A new interpretation of floral morphology in Garrya
(Garryaceae). Taxon 52: 271 276.
Oxelman, B., Yoshikawa, N., McConaughy, B.L., Luo, J., Denton, A.L., &
Hall, B.D. 2004. RPB2 gene phylogeny in flowering plants, with particular
emphasis on asterids. Molecular Phylogenetics and Evolution 32: 462-479.
Tree ferns occur throughout the world in predominantly tropical habitats. The
group has a long history and is known since the Jurassic, ca. 160 million
years ago. Fossils of this family, Cyatheaceae, are usually carbon imprints
(called compression fossils) of leaves. Other fossils, such as the stems
of tree ferns, are petrified, with the organic plant material mostly replaced
by minerals. This image of the indusium of Cyathea cranhamii Smith,
Rothwell et Stockey shows sporangia with spores. Spores are triangular with
a trilete mark. The sporangia have areas with thickened cell walls (the
annulus), which help in dehiscence (the opening of the sporangium) and spore
dispersal. Sporangial stalks are visible as small clusters of four to six
cells in cross section. Cyathea cranhamii comes from late Cretaceous
(ca. 130 million years ago) sediments of British Columbia, Canada and represents
the first known permineralized reproductive tree fern material.
This is a photograph of Ledothamnus sessiliflorus N.E. Brown (Ericaceae: blueberry family). The genus of seven species (Luteyn 1995) is found only in the Guiana Highlands of northern South America, a region known for its pristine habitat and highly endemic flora. Ledothamnus was thought to be endemic to tepui summits of the Venezuelan Guyana. During the summer of 2004, it was collected in Guyana by Dr. David Clarke (Univ. of North Carolina-Asheville), Stephen Stern (Univ. of Utah), Diana Gittens (Univ. of Guyana), Amerindian collaborators, and myself from the summit of Mt. Maringma. Maringma, slightly east of Mt. Roraima, is the highest tepui wholly within Guyana (2200 m / 7200 ft.) and was previously unexplored biologically. Its tepui summit hosts genuine cloud forests characterized by quaking bogs, rocky outcrops, and dense, tangled vegetation. At 5
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