ASTERACEAE: CHARACTERISTICS, HABITAT, SPECIES AND USES - BIOLOGY - 2024

The Asteraceae family (also known as Compositae) is the most diverse of the angiosperms, containing approximately 1,620 genera and more than 23,600 species. This family is distributed throughout the world, except in the Antarctic region.

Asteraceae are especially diverse in tropical and subtropical regions around the world. They are generally herbaceous plants that grow wild in North America, the Andes, the Amazon rainforest, Africa, the Mediterranean region, and Asia.

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Most members of the Asteraceae family have herbaceous growth. However, an important group of these plants is made up of shrubs and trees that occur in the tropical regions of North and South America, Africa, Madagascar, and the islands of the Atlantic and Pacific Oceans.

The asteraceae or sunflower family, as they are also known, are generally ruderal plants, and they abound in disturbed areas. However, a significant number of them are in danger of extinction, especially those that inhabit mountainous regions of the tropics.

The Asteraceae family contains members that are important as sources of cooking oil, sweetening agents, and as tea infusions. In addition, several members are popularly known for their horticultural value, which is why they are grown in gardens.

However, members of the Asteraceae family do not escape the attack of several phytopathogens. The disease that has the greatest impact on asteraceae is that of aster yellows, which can be caused by a phytoplasma.

characteristics

The term Asteraceae is due to the distinctive characteristics of the inflorescence structures. Above all, the highly compressed branch system of the inflorescence, called the flower head or flower head. In the chapter all the flowers are attached to a receptacle that is surrounded by involucre bracts.

In turn, the chapter forms a pseudanth, a type of inflorescence that resembles a large flower. Other characteristics that distinguish the family include the anthers attached to a tube and the inferior position of the ovary.

In fact, the Asteraceae family differs from the rest mainly by the characteristics of its inflorescence.

The chapter

The flower heads or chapters of the asteraceae can be homogamous or heterogamous. In the homogamous chapters all the flowers are the same, while in the heterogamous chapters, the margin flowers are morphologically and functionally different from the flowers located in the center.

The marginal flowers of the heterogamous capitula can be sterile or female, and have striking petals with bilateral symmetry (zygomorphs). While the flowers of the central disc are hermaphrodites with functional stamens and carpels, with modest petals, and often radially symmetrical (actinomorphic).

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Corolla

There are six types of corollas present in the Asteraceae family, two of which are actinomorphic and the other four are zygomorphic. Actinomorphic corollas are composed of five equal lobes and are called disk corollas (because they occupy most of the disk).

The tubular corollas are closely actinomorphic, and in most cases they lack stamens. In turn, they are considered the ancestral corollas of the asteraceae. For their part, zygomorphic corollas are generally limited to the first row of florets in the capitulum, although some species may have several rows of zygomorphic corollas.

Bilabiated corollas generally occur only in several genera of ancestral subfamilies, such as Barnadesioideae and Mutisieae. This type of zygomorphic corolla has a 3 + 2 lobed arrangement, with the 3-lobed lamina facing outward and the 2-lobed lamina toward the center of the capitulum.

Archives chapter. Bruce marlin

The pseudo bilabiate corolla has a 4 + 1 lobed arrangement. While the ray flower consists of a 2 to 3-lobed lamina. The ligule corollas have 5 lobes.

Anthers

Many asteraceae flowers have five anthers corresponding to the number of lobes on the corolla. The anthers are positioned alternately along the sinuses of the corolla lobes. The anther filaments are free from the corolla just above the tube, while the two thecae of each stamen are connected with the thecae of the adjacent stamens producing a tube surrounding the style.

Pollen is shed into each tube (dehiscent intrusion). On the other hand, the connective (tissue that joins the two thecas) can produce an appendix. Also, the neck of the anther is relatively shorter on the adaxial side towards the style.

Theca may extend below the point of insertion between the filament and the connective (anther calcarate). Anthers of this type and with tails are very common among the primitive members of this family.

Leaves

Asteraceae leaves are generally opposite or alternate. Sometimes they are organized in basal rosettes, and rarely in whorls. The stipulation occurs infrequently. While the leaves are usually petiolate, and sometimes sessile. Also, the leaves are simple and rarely compound.

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Fruit

Plants in the Asteraceae family produce dry, indehiscent fruits called cysela or achenes. Some species have fleshy fruits that look like a drupe. Also, most species have a modified calyx that serves as protection against herbivores. The fruits have an exalbuminated seed and a straight embryo.

Tragopogon porrifolius (Goat's Beard): Post anthesis chapter; detail of the cipselas. Philmarin

Habitat and distribution

The species that make up the Asteraceae family are cosmopolitan, being restricted only in the Antarctic region. They make up the greatest diversity of angiosperms on the planet, especially in tropical regions.

They are plants resistant to various abiotic conditions, being found in disturbed places. Furthermore, they are frequent in number of species or number of individuals in open arid and semi-arid regions.

Taxonomy

The initial classification of the Compositae family was developed by Cassini in 1819, who grouped the genera into tribes. Later the grouping of the tribes in subfamily took place and the subfamilies Cichorioideae and Asteroideae arose. To define these two groups, morphological characteristics such as the discontinuity in the corolla, anther, and the morphology of the style were taken.

Asteroideae are characterized by having a ray flower, short-lobed disk corollas, and caveed pollen.

With the addition of DNA sequence analysis, the classification of Asteraceae has changed; mainly due to the recognition of the monophyletic groups included in the clade Cichorioideae.

The Asteraceae family classification is dominated by the Asteroideae subfamily, which contains more than 70% of the species in the family. The other subfamilies include Carduoideae and Cichorioideae, each containing more than 2,000 species. The other subfamilies contain less than 1000 species, and the Gymnarrhenoideae and Hecastocleidoideae subfamilies contain one species each.

Representative species

The Asteraceae family contains more than 1,320 genera and 23600 species worldwide. However, several of its species are representative, among which we can mention the sunflower (Helianthus annuus), the gerbera (Gerbera jamesonii), and the stevia (Stevia rebaudiana), among others.

Helianthus annuus (sunflower) is part of the Asteroideae subfamily, and has straight stems that can measure up to 2 meters. It is native to North and Central America, and is frequently used for the extraction of cooking oil.

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For its part, the gerbera is a herbaceous plant in the form of a rosette, which belongs to the subfamily Mutisioideae. It is an ornamental plant that is native to South Africa.

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While Stevia rebaudiana is a small herbaceous plant, with alternate leaves, which is used as a sweetener. This plant is part of the Asteroideae subfamily and is native to South America.

Stevia rebaudiana. Ethel Aardvark

Applications

Several species of asteraceae are important, for the socioeconomic contributions they make when cultivated. Thus, many species are used by various cultures around the world, especially in traditional medicine.

From an economic point of view, asteraceae are exploited to obtain cooking oils, such as black seed oil (obtained from Guizotia abyssinica), safflower oil (obtained from Carthamus tinctorius) and sunflower oil (from Helianthus annuus).

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The foods obtained from plants of the Asteraceae family are artichoke (Cynara cardunculus), endive (Cichorium endivia), topinambur (Helianthus tuberosus), lettuce (Lactuca sativa), Mexican tarragon (Tagetes lucida), radicchio (Cichorium intybus), salsify (Tragopogon porrifolius), sunflower seeds (Helianthus annuus), and tarragon (Artemisia dracunculus).

Ornamental plants include black-eyed susan (Rudbeckia hirta), chrysanthemum (Chrysanthemum sp.), Dahlias (Dahlias coccinea), calendula (Tagetes erecta), and gerbera (Gerbera jamesonii), among others.

Likewise, many species of asteraceae are used as antimalarials and as antileishmaniasis. From an industrial point of view, asteraceae are used to obtain flavorings for beverages, to obtain colorants, for the manufacture of rubbers, etc.

Diseases

The disease that most affects members of the Asteraceae family is aster yellow, which is caused by the phytoplasma Callistephus chinensis. The most recurrent symptoms are chlorotic leaves, abnormal branching, and interruption of flowering.

In turn, gray mold can also affect various species of Asteraceae. This disease is caused by the necrotrophic pathogen Botrytis cinerea, and is characterized by producing brown spots (necrosis) on petals that ultimately lead to certain death of the flower.

Meanwhile Fusarium wilt, which is the result of infection with the pathogen Fusarium oxysporum, is fatal to seedlings. In addition, infected adult plants show severe symptoms of chlorosis, leading to widespread wilting in the long term.

Other diseases include leaf spots caused by Alternaria spp., Ascophyta spp., Cercospora spp., And Septoria spp., Downy mildew (Golovinomyces cichoracearum, as the causative agent), and rot (caused by Coleosporium solidaginis).

References

1. Bessada, SMF, Barreira, JCM, Oliveira, MBP 2015. Asteraceae species with most prominent bioactivity and their potential applications: A review. Industrial Crops and Products, 76: 604–615.
2. Elomaa, P., Zhao, Y., Zhang, T. 2018. Flower heads in Asteraceae-recruitment of conserved developmental regulators to control the flower-like inflorescence architecture. Horticulture Research, 5 (36): 1-10.
3. Flora of North America. Composite Family. Taken from efloras.org.
4. Master Gardener Program Division of Extension (2015). Aster Yellows. Taken from wimastergardener.org
5. Penn State Extension (2019). Aster Diseases. Taken from extension.psu.edu.
6. ScienceDirect. Molecular Control of Inflorescence Development in Asteraceae. Taken from sciencedirect.com.
7. Shi, Z. et al.. 2011. Asteraceae (Compositae). Flora of China, 20: 1-8.
8. The Tree of Life Web Project (1995-2004). Asteraceae. Sunflowers, daisies. Taken from tolweb.org.
9. The Tree of Life Web Project (1995-2004). Economically Important Sunflowers. Taken from tolweb.org
10. Zareh, MM 2005. Synopsis of the Family Asteraceae in Egypt. International Journal of Agriculture & Biology, 7 (5): 832-844.