Simsia
Encyclopedia
Simsia is a genus
of flowering plant
s in the family Asteraceae
. It comprises 23 species that include annuals
, herbaceous
perennials
, and shrub
s. The genus is widespread geographically, and though the greatest diversity of species occurs in Mexico
, it ranges as far north as the western United States
and south through Central America
to South America
, where there are two endemic species, one of which extends as far as Argentina
. Although some species are relatively rare, others have become common weeds that line the roadsides and fields of Mexico, often forming dense stands mixed with Tithonia
and other Asteraceae.
The genus was thoroughly studied by Spooner using comparative morphology, chromosome counts, and crossing exeriments, and based on samples from wide-ranging field work. Subsequently two new species have been documented , and additional species are being transferred into the genus. Although at one time, Simsia was considered to be related to other genera with flattened cypselae, such as Encelia
, it is now firmly established that Simsia is part of subtribe Helianthinae (the taxonomic group which includes the common sunflower, Helianthus annuus), and is a close relative of Tithonia .
All of the species for which chromosome counts have been made are diploid (x = 17), and crossing experiments suggest that there are few barriers to hybridization between species of the genus. Natural hybridization appears to occur and may complicate identification of some specimens, particularly involving the weedy species such as S. foetida, S. amplexicaulis, and S. lagascaeformis.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of flowering plant
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
s in the family Asteraceae
Asteraceae
The Asteraceae or Compositae , is an exceedingly large and widespread family of vascular plants. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies...
. It comprises 23 species that include annuals
Annual plant
An annual plant is a plant that usually germinates, flowers, and dies in a year or season. True annuals will only live longer than a year if they are prevented from setting seed...
, herbaceous
Herbaceous plant
A herbaceous plant is a plant that has leaves and stems that die down at the end of the growing season to the soil level. They have no persistent woody stem above ground...
perennials
Perennial plant
A perennial plant or simply perennial is a plant that lives for more than two years. The term is often used to differentiate a plant from shorter lived annuals and biennials. The term is sometimes misused by commercial gardeners or horticulturalists to describe only herbaceous perennials...
, and shrub
Shrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...
s. The genus is widespread geographically, and though the greatest diversity of species occurs in Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
, it ranges as far north as the western United States
Western United States
.The Western United States, commonly referred to as the American West or simply "the West," traditionally refers to the region comprising the westernmost states of the United States. Because the U.S. expanded westward after its founding, the meaning of the West has evolved over time...
and south through Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
to South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
, where there are two endemic species, one of which extends as far as Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
. Although some species are relatively rare, others have become common weeds that line the roadsides and fields of Mexico, often forming dense stands mixed with Tithonia
Tithonia
Tithonia is a genus of flowering plants in the family Asteraceae. It includes 11 species, with a center of distribution in Mexico but with one species extending into the Southwestern United States and several extending into Central America. Two species, T. diversifolia and T...
and other Asteraceae.
Description and systematics
A feature that characterizes many of the species of the genus and helps to distinguish them from related genera is the extremely flattened cypsela (achene). There are, however, several species in which the cypsela is biconvex, and these are recognized as belonging to Simsia by a group of other, mostly technical features, including nodal disks (stipule-like appendages at the base of the petioles), relatively long and narrow ray ovaries, and long and tapering style branches that lack a pronounced apical appendage.The genus was thoroughly studied by Spooner using comparative morphology, chromosome counts, and crossing exeriments, and based on samples from wide-ranging field work. Subsequently two new species have been documented , and additional species are being transferred into the genus. Although at one time, Simsia was considered to be related to other genera with flattened cypselae, such as Encelia
Encelia
Encelia is a genus of the plant family Asteraceae. It consists of shrubs of arid environments in southwestern North America and western South America. All have n = 18 chromosomes. With the exception of the South American species, all are obligate outcrossers...
, it is now firmly established that Simsia is part of subtribe Helianthinae (the taxonomic group which includes the common sunflower, Helianthus annuus), and is a close relative of Tithonia .
All of the species for which chromosome counts have been made are diploid (x = 17), and crossing experiments suggest that there are few barriers to hybridization between species of the genus. Natural hybridization appears to occur and may complicate identification of some specimens, particularly involving the weedy species such as S. foetida, S. amplexicaulis, and S. lagascaeformis.
Selected species
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Formerly placed here
- Encelia frutescensEncelia frutescensEncelia frutescens is a species of flowering plant in the daisy family known by the common names button brittlebush and bush encelia.-Distribution:...
(A.Gray) A.Gray (as S. frutescens A.Gray)