The tropics are the regions of Earth surrounding the Equator , where the sun may shine directly overhead . This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's axial tilt ; the width of the tropics (in latitude) is twice the tilt. The tropics are also referred to as the tropical zone and the torrid zone (see geographical zone ).
55-701: Eutrochium is a North American genus of herbaceous flowering plants in the family Asteraceae . They are commonly referred to as Joe-Pye weeds . They are native to the United States and Canada, and have non-dissected foliage and pigmented flowers. The genus includes all the purple-flowering North American species of the genus Eupatorium as traditionally defined, and most are grown as ornamental plants , particularly in Europe and North America. Eupatorium has recently undergone some revision and has been broken up into smaller genera. Joe Pye weeds were initially included in
110-512: A " celestial body with rays". The capitulum, which often appears to be a single flower, is often referred to as a head . In some species, the entire head is able to pivot its floral stem in the course of the day to track the sun (like a "smart" solar panel), thus maximizing the reflectivity of the entire floral unit and further attracting flying pollinators. Nearest to the flower stem lie a series of small, usually green, scale-like bracts . These are known as phyllaries ; collectively, they form
165-506: A 3+2 scheme – above the fused corolla tube, three very long fused petals form the ligule, with the other two petals being inconspicuously small. The Cichorioideae has only ray florets, with a 5+0 scheme – all five petals form the ligule. A 4+1 scheme is found in the Barnadesioideae. The tip of the ligule is often divided into teeth, each one representing a petal. Some marginal florets may have no petals at all (filiform floret). The calyx of
220-499: A break in rainfall during mid-season when the Intertropical Convergence Zone or monsoon trough moves poleward of their location during the middle of the warm season; Typical vegetation in these areas ranges from moist seasonal tropical forests to savannahs . When the wet season occurs during the warm season, or summer , precipitation falls mainly during the late afternoon and early evening hours. The wet season
275-448: A few unusual species, the "head" will consist of one single disc flower; alternatively, a few species will produce both single-flowered female heads, along with multi-flowered male heads, in their "pollination strategy". The distinguishing characteristic of Asteraceae is their inflorescence , a type of specialised, composite flower head or pseudanthium , technically called a calathium or capitulum , that may look superficially like
330-428: A scarious (dry and membranous) texture. The phyllaries can be free or fused, and arranged in one to many rows, overlapping like the tiles of a roof ( imbricate ) or not (this variation is important in identification of tribes and genera). Each floret may be subtended by a bract, called a "palea" or "receptacular bract". These bracts are often called " chaff ". The presence or absence of these bracts, their distribution on
385-476: A single floral entity is in fact a composite of much smaller flowers. The "petals" or "sunrays" in an "asteraceous" head are in fact individual strap-shaped flowers called ray flowers or ray florets , and the "sun disk" is made up of smaller, radially symmetric , individual flowers called disc flowers or disc florets . The word aster means "star" in Greek, referring to the appearance of most family members as
440-441: A single flower. The capitulum is a contracted raceme composed of numerous individual sessile flowers , called florets , all sharing the same receptacle . A set of bracts forms an involucre surrounding the base of the capitulum. These are called "phyllaries", or "involucral bracts". They may simulate the sepals of the pseudanthium. These are mostly herbaceous but can also be brightly coloured (e.g. Helichrysum ) or have
495-420: A sort of tube around the style ( theca ). They commonly have basal and/or apical appendages. Pollen is released inside the tube and is collected around the growing style, and then, as the style elongates, is pushed out of the tube ( nüdelspritze ). The pistil consists of two connate carpels . The style has two lobes. Stigmatic tissue may be located in the interior surface or form two lateral lines. The ovary
550-585: A stem node age of 88–89 mya (Late Cretaceous, Coniacian ). Asteraceae is an economically important family, providing food staples, garden plants, and herbal medicines. Species outside of their native ranges can become weedy or invasive . Members of the Asteraceae are mostly herbaceous plants, but some shrubs, vines, and trees (such as Lachanodes arborea ) do exist. Asteraceae species are generally easy to distinguish from other plants because of their unique inflorescence and other shared characteristics, such as
605-477: Is a large family of flowering plants that consists of over 32,000 known species in over 1,900 genera within the order Asterales . The number of species in Asteraceae is rivaled only by the Orchidaceae , and which is the larger family is unclear as the quantity of extant species in each family is unknown. The Asteraceae were first described in the year 1740 and given the original name Compositae . The family
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#1733085127638660-500: Is a time when air quality improves, freshwater quality improves and vegetation grows significantly due to the wet season supplementing flora, leading to crop yields late in the season. Floods and rains cause rivers to overflow their banks, and some animals to retreat to higher ground. Soil nutrients are washed away and erosion increases. The incidence of malaria increases in areas where the rainy season coincides with high temperatures. Animals have adaptation and survival strategies for
715-414: Is a two- or three-lobed, strap-shaped, individual flower, found in the head of most members of the Asteraceae. The corolla of the ray flower may have two tiny, vestigial teeth, opposite to the three-lobed strap, or tongue, indicating its evolution by fusion from an ancestral, five-part corolla. In some species, the 3:2 arrangement is reversed, with two lobes, and zero or three tiny teeth visible opposite
770-411: Is actually a composite of several much smaller flowers, known as the capitulum or head . By visually presenting as a single flower, the capitulum functions in attracting pollinators , in the same manner that other "showy" flowering plants in numerous other, older, plant families have evolved to attract pollinators. The previous name for the family, Compositae , reflects the fact that what appears to be
825-533: Is an advantage in relatively dry zones, or some combination of these and possibly other factors. Heterocarpy, or the ability to produce different fruit morphs, has evolved and is common in Asteraceae. It allows seeds to be dispersed over varying distances and each is adapted to different environments, increasing chances of survival. The original name Compositae is still valid under the International Code of Nomenclature for algae, fungi, and plants. It refers to
880-1370: Is based on Panero & Funk (2002) updated in 2014, and now also includes the monotypic Famatinanthoideae . The diamond (♦) denotes a very poorly supported node (<50% bootstrap support), the dot (•) a poorly supported node (<80%). Barnadesioideae : 9 genera, 93 species. South America , mainly the Andes . Famatinanthoideae : South America, 1 genus, 1 species Famatinanthus decussatus . Mutisioideae : 58 genera, 750 species. Absent from Europe, mostly in South America. Stifftioideae : 10 genera. South America. Wunderlichioideae : 8 genera, 24 species. Mostly in Venezuela and Guyana . Gochnatioideae : 4 or 5 genera, 90 species. Latin America and southern United States. Hecastocleidoideae : Only Hecastocleis shockleyi . Southwestern United States . Carduoideae : 83 genera, 2,500 species. Worldwide. Pertyoideae : 5 or 6 genera, 70 species. Asia. Gymnarrhenoideae : Two genera/species, Gymnarrhena micrantha ( Northern Africa , Middle East ) and Cavea tanguensis ( Eastern Himalayas ). Cichorioideae : 224 genera, 3,200 species. Worldwide. Corymbioideae : Only
935-503: Is commonly known as the aster , daisy , composite , or sunflower family . Most species of Asteraceae are herbaceous plants , and may be annual , biennial , or perennial , but there are also shrubs , vines , and trees . The family has a widespread distribution, from subpolar to tropical regions , in a wide variety of habitats. Most occur in hot desert and cold or hot semi-desert climates , and they are found on every continent but Antarctica . Their common primary characteristic
990-526: Is compound flower heads , technically known as capitula , consisting of sometimes hundreds of tiny individual florets enclosed by a whorl of protective involucral bracts . The oldest known fossils are pollen grains from the Late Cretaceous ( Campanian to Maastrichtian ) of Antarctica, dated to c. 76–66 million years ago (mya). It is estimated that the crown group of Asteraceae evolved at least 85.9 mya (Late Cretaceous, Santonian ) with
1045-450: Is inferior and has only one ovule , with basal placentation . In members of the Asteraceae the fruit is achene -like, and is called a cypsela (plural cypselae ). Although there are two fused carpels, there is only one locule, and only one seed per fruit is formed. It may sometimes be winged or spiny because the pappus, which is derived from calyx tissue often remains on the fruit (for example in dandelion ). In some species, however,
1100-585: Is that the tropics represent a ' Garden of Eden ', a heaven on Earth, a land of rich biodiversity or a tropical paradise. The alternative is that the tropics consist of wild, unconquerable nature. The latter view was often discussed in old Western literature more so than the first. Evidence suggests over time that the view of the tropics as such in popular literature has been supplanted by more well-rounded and sophisticated interpretations. Western scholars tried to theorise why tropical areas were relatively more inhospitable to human civilisations than colder regions of
1155-512: Is the only kind of floret in the Carduoideae , while the first kind is more widespread. Ray florets are always highly zygomorphic and are characterised by the presence of a ligule , a strap-shaped structure on the edge of the corolla tube consisting of fused petals. In the Asteroideae and other minor subfamilies these are usually borne only on florets at the circumference of the capitulum and have
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#17330851276381210-542: The Andes as far south as the northernmost parts of Chile and Perú . The climate is changing in the tropics, as it is in the rest of the world. The effects of steadily rising concentrations of greenhouse gases on the climate may be less obvious to tropical residents, however, because they are overlain by considerable natural variability. Much of this variability is driven by the El Niño-Southern Oscillation (ENSO) . The Tropics has warmed by 0.7–0.8 °C over
1265-703: The Pantropic . The system of biogeographic realms differs somewhat; the Neotropical realm includes both the Neotropics and temperate South America, and the Paleotropics correspond to the Afrotropical , Indomalayan , Oceanian , and tropical Australasian realms . Flora are plants found in a specific region at a specific time. Some well-known plants that are exclusively found in, originate from, or are often associated with
1320-570: The Waterberg Biosphere of South Africa , and eastern Madagascar rainforests. Often the soils of tropical forests are low in nutrient content, making them quite vulnerable to slash-and-burn deforestation techniques, which are sometimes an element of shifting cultivation agricultural systems. In biogeography , the tropics are divided into Paleotropics (Africa, Asia and Australia) and Neotropics (Caribbean, Central America, and South America). Together, they are sometimes referred to as
1375-696: The axial tilt of the Earth . The Tropic of Cancer is the Northernmost latitude from which the Sun can ever be seen directly overhead , and the Tropic of Capricorn is the Southernmost. This means that the tropical zone includes everywhere on Earth which is a subsolar point at least once during the solar year . Thus the maximum latitudes of the tropics have equal distances from the equator on either side. Likewise, they approximate
1430-432: The involucre , which serves to protect the immature head of florets during its development. The individual florets are arranged atop a dome-like structure called the receptacle . The individual florets in a head consist, developmentally, of five fused petals (rarely four); instead of sepals , they have threadlike, hairy, or bristly structures, known collectively as a pappus , (plural pappi ). The pappus surrounds
1485-400: The "composite" nature of the capitula, which consist of a few or many individual flowers. Tropical regions Due to the overhead sun, the tropics receive the most solar energy over the course of the year, and consequently have the highest temperatures on the planet. Even when not directly overhead, the sun is still close to overhead throughout the year, therefore the tropics also have
1540-399: The angle of the Earth's axial tilt. This angle is not perfectly fixed, mainly due to the influence of the moon, but the limits of the tropics are a geographic convention, and their variance from the true latitudes is very small. Many tropical areas have both a dry and a wet season. The wet season , rainy season or green season is the time of year, ranging from one or more months when most of
1595-455: The average annual rainfall in a region falls. Areas with wet seasons are disseminated across portions of the tropics and subtropics , some even in temperate regions. Under the Köppen climate classification , for tropical climates , a wet-season month is defined as one or more months where average precipitation is 60 mm (2.4 in) or more. Some areas with pronounced rainy seasons see
1650-625: The disc in irregular symmetry, or with a weakly bilaterally symmetric arrangement. A radiate head has disc flowers surrounded by ray flowers. A ligulate head has all ligulate flowers and no disc flowers. When an Asteraceae flower head has only disc flowers that are either sterile, male, or bisexual (but not female and fertile), it is a discoid head . Disciform heads possess only disc flowers in their heads, but may produce two different sex types (male or female) within their disciform head. Some other species produce two different head types: staminate (all-male), or pistillate (all-female). In
1705-613: The energy store is generally in the form of inulin rather than starch. They produce iso/ chlorogenic acid , sesquiterpene lactones , pentacyclic triterpene alcohols, various alkaloids , acetylenes (cyclic, aromatic, with vinyl end groups), tannins . They have terpenoid essential oils that never contain iridoids . Asteraceae produce secondary metabolites , such as flavonoids and terpenoids . Some of these molecules can inhibit protozoan parasites such as Plasmodium , Trypanosoma , Leishmania and parasitic intestinal worms, and thus have potential in medicine. Compositae,
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1760-422: The extant genus Dasyphyllum . Barreda, et al. (2015) estimated that the crown group of Asteraceae evolved at least 85.9 mya (Late Cretaceous, Santonian ) with a stem node age of 88–89 mya (Late Cretaceous, Coniacian ). It is not known whether the precise cause of their great success was the development of the highly specialised capitulum, their ability to store energy as fructans (mainly inulin ), which
1815-425: The florets may be absent, but when present is always modified into a pappus of two or more teeth, scales or bristles and this is often involved in the dispersion of the seeds. As with the bracts, the nature of the pappus is an important diagnostic feature. There are usually four or five stamens . The filaments are fused to the corolla, while the anthers are generally connate ( syngenesious anthers), thus forming
1870-549: The genus Corymbium , with 9 species. Cape provinces, South Africa. Asteroideae : 1,130 genera and 16,200 species. Worldwide. The family includes over 32,000 currently accepted species, in over 1,900 genera ( list ) in 13 subfamilies. The number of species in the family Asteraceae is rivaled only by Orchidaceae. Which is the larger family is unclear, because of the uncertainty about how many extant species each family includes. The four subfamilies Asteroideae , Cichorioideae , Carduoideae and Mutisioideae contain 99% of
1925-568: The genus Eupatoriadelphus in Eupatorium , while recognizing this former genus as being the same group of plants as Rafinesque's Eutrochium . This decision was also widely accepted. Based on chloroplast DNA analysis published by Edward E, Schilling et al. in 1999, the Joe Pye weeds were again separated into their own genus, Eutrochium , as Eutrochium is the senior synonym of Eupatoriadelphus . This usage quickly became formalized. Eupatorium in
1980-430: The genus Eupatorium , but as early as the 19th century Franco-American botanist Constantine Samuel Rafinesque proposed separating them into their own genus Eutrochium . Unaware of this, research botanists Robert M. King and Harold Robinson proposed assigning them to a new genus Eupatoriadelphus in 1970. This was widely accepted, and Joe Pye weeds began to be referred to as such. In 1987, Robinson and King reincluded
2035-456: The geographic region; these usages ought not be confused. The Earth's axial tilt is currently around 23.4° , and therefore so are the latitudes of the tropical circles , marking the boundary of the tropics: specifically, ±23°26′09.8″ (or 23.43605°). The northern one is called the Tropic of Cancer , and the southern is the Tropic of Capricorn . As the Earth's axial tilt changes, so too do
2090-424: The joined anthers of the stamens . Nonetheless, determining genera and species of some groups such as Hieracium is notoriously difficult (see " damned yellow composite " for example). Members of the family Asteraceae generally produce taproots , but sometimes they possess fibrous root systems. Some species have underground stems in the form of caudices or rhizomes . These can be fleshy or woody depending on
2145-955: The last century—only slightly less than the global average—but a strong El Niño made 1998 the warmest year in most areas, with no significant warming since. Climate models predict a further 1–2 °C warming by 2050 and 1–4 °C by 2100. Tropical plants and animals are those species native to the tropics. Tropical ecosystems may consist of tropical rainforests , seasonal tropical forests , dry (often deciduous) forests , spiny forests, deserts , savannahs, grasslands and other habitat types. There are often wide areas of biodiversity , and species endemism present, particularly in rainforests and seasonal forests. Some examples of important biodiversity and high-endemism ecosystems are El Yunque National Forest in Puerto Rico , Costa Rican and Nicaraguan rainforests, Amazon Rainforest territories of several South American countries, Madagascar dry deciduous forests ,
2200-424: The leaves. Nearly all Asteraceae bear their flowers in dense flower heads called capitula . They are surrounded by involucral bracts , and when viewed from a distance, each capitulum may appear to be a single flower. Enlarged outer (peripheral) flowers in the capitulum may resemble petals, and the involucral bracts may look like a calyx. In plants of the Asteraceae, what appears to be a single "daisy"-type flower
2255-445: The lowest seasonal variation on the planet; "winter" and "summer" lose their contrast. Instead, seasons are more commonly divided by precipitation variations than by temperature variations. The tropics maintain wide diversity of local climates, such as rain forests , monsoons , savannahs , deserts , and high altitude snow-capped mountains . The word "tropical" can specifically refer to certain kinds of weather , rather than to
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2310-473: The original name for Asteraceae, were first described in 1740 by Dutch botanist Adriaan van Royen . Traditionally, two subfamilies were recognised: Asteroideae (or Tubuliflorae) and Cichorioideae (or Liguliflorae). The latter has been shown to be extensively paraphyletic , and has now been divided into 12 subfamilies, but the former still stands. The study of this family is known as synantherology . The phylogenetic tree of subfamilies presented below
2365-434: The ovary and can, when mature and attached to a seed, adhere to animal fur or be carried by air currents, aiding in seed dispersal . The whitish, fluffy head of a dandelion , commonly blown on by children, consists of numerous seeds resting on the receptacle, each seed attached to its pappus. The pappi provide a parachute-like structure to help the seed travel from its point of origin to a more hospitable site. A ray flower
2420-465: The pappus falls off (for example in Helianthus ). Cypsela morphology is often used to help determine plant relationships at the genus and species level. The mature seeds usually have little endosperm or none. The pollen of composites is typically echinolophate, a morphological term meaning "with elaborate systems of ridges and spines dispersed around and between the apertures." In Asteraceae,
2475-440: The receptacle, and their size and shape are all important diagnostic characteristics for genera and tribes. The florets have five petals fused at the base to form a corolla tube and they may be either actinomorphic or zygomorphic . Disc florets are usually actinomorphic, with five petal lips on the rim of the corolla tube. The petal lips may be either very short, or long, in which case they form deeply lobed petals. The latter
2530-532: The revised sense (about 42 species of white-flowered plants from the temperate Northern hemisphere ) is apparently a close relative of Eutrochium . In addition to flower color, another difference between Eutrochium and Eupatorium is that the former has mostly whorled leaves and the latter mostly opposite ones. Eupatorium and Eutrochium are both placed in the subtribe Eupatoriinae, but South American plants which have sometimes been placed in that subtribe, such as Stomatanthes , seem to belong elsewhere in
2585-499: The species diversity of the whole family (approximately 70%, 14%, 11% and 3% respectively). Because of the morphological complexity exhibited by this family, agreeing on generic circumscriptions has often been difficult for taxonomists . As a result, several of these genera have required multiple revisions. The oldest known fossils of members of Asteraceae are pollen grains from the Late Cretaceous of Antarctica , dated to ~76–66 mya ( Campanian to Maastrichtian ) and assigned to
2640-576: The species. The stems are herbaceous, aerial, branched, and cylindrical with glandular hairs, usually erect, but can be prostrate to ascending. The stems can contain secretory canals with resin , or latex , which is particularly common among the Cichorioideae . Leaves can be alternate , opposite , or whorled . They may be simple , but are often deeply lobed or otherwise incised, often conduplicate or revolute . The margins also can be entire or toothed . Resin or latex can also be present in
2695-446: The tongue. A ligulate flower is a five-lobed, strap-shaped, individual flower found in the heads of certain other asteraceous species. A ligule is the strap-shaped tongue of the corolla of either a ray flower or of a ligulate flower. A disk flower (or disc flower ) is a radially symmetric individual flower in the head, which is ringed by the ray flowers when both are present. In some species, ray flowers may be arranged around
2750-413: The tribe Eupatorieae . All of the Joe Pye weed species except E. steelei are widely cultivated as ornamental landscape plants. Cultivars have been developed for a more compact habit (e.g. E. dubium ‘Little Joe’, E. dubium ‘Baby Joe’, E. maculatum ‘Little Red’) and varied flower color. Joe Pye weeds have traditionally been ascribed with medicinal powers. A peer-reviewed study suggests that Joe Pye
2805-516: The tropical and polar circles . The tropics constitute 39.8% of Earth's surface area and contain 36% of Earth's landmass . As of 2014 , the region was home also to 40% of the world's population , and this figure was then projected to reach 50% by 2050. Because of global warming , the weather conditions of the tropics are expanding with areas in the subtropics , having more extreme weather events such as heatwaves and more intense storms. These changes in weather conditions may make certain parts of
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#17330851276382860-464: The tropics include: Tropicality refers to the image of the tropics that people from outside the tropics have of the region, ranging from critical to verging on fetishism. Tropicality gained renewed interest in geographical discourse when French geographer Pierre Gourou published Les pays tropicaux ( The Tropical World in English), in the late 1940s. Tropicality encompassed two major images. One,
2915-550: The tropics uninhabitable. The word "tropic" comes via Latin from Ancient Greek τροπή ( tropē ), meaning "to turn" or "change direction". The tropics are defined as the region between the Tropic of Cancer in the Northern Hemisphere at 23°26′09.8″ (or 23.43605°) N and the Tropic of Capricorn in the Southern Hemisphere at 23°26′09.8″ (or 23.43605°) S; these latitudes correspond to
2970-708: The wetter regime. The previous dry season leads to food shortages into the wet season, as the crops have yet to mature. However, regions within the tropics may well not have a tropical climate. Under the Köppen climate classification, much of the area within the geographical tropics is classed not as "tropical" but as "dry" ( arid or semi-arid ), including the Sahara Desert , the Atacama Desert and Australian Outback . Also, there are alpine tundra and snow-capped peaks, including Mauna Kea , Mount Kilimanjaro , Puncak Jaya and
3025-507: Was a Mohican sachem named Schauquethqueat who lived in the mission town of Stockbridge, Massachusetts from c. 1740 to c. 1785 and who took as his Christian name, Joseph Pye. Sources (although without citation) claim the plant was used to treat typhus outbreaks and for the treatment of kidney stones and other urinary tract ailments. [REDACTED] Media related to Eutrochium at Wikimedia Commons Asteraceae Asteraceae ( / ˌ æ s t ə ˈ r eɪ s i . iː , - ˌ aɪ / )
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