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Landslides, floods, earthquakes, droughts, fires and volcanic eruptions are natural factors which historically have influenced the distribution and species composition of plant communities. In fact, some communities are adapted to periodic natural disruptions: chaparral communities depend on fire for renewal, and some riparian communities require periodic flooding. However, not all disruptions are natural nor are native plant communities adapted to or, much less, dependent on them for survival. Communities which are born of the repeated disruption of natural habitats by humans are called anthropogenic, human-generated. Until just over 200 years ago, California did not know intensive European-style agriculture or mass urbanization. When Europeans came to California, the population of Native Californians was approximately 300,000. Today there are almost 100 times as many people. And if sheer numbers were not sufficient impact on the natural resources, also "present human demands on the environment are drastically different from those of the past. Traditional technologies of original California peoples were based on the philosophy of resource conservation and renewal. Use of their sophisticated technologies meant modest impact on the ecosystem. In contrast, European technologies are based on an agricultural economy that changes wildness to a homogeneous, managed landscape. The diversity of native vegetation, animals, and cultures is threatened by this philosophy and practice..."

Anthropogenic communities have arisen from two main types of disruption: agricultural (pastoral and agrestal) and urban (e.g., roadsides, trails, and empty lots). The plants that grow in these areas are primarily Mediterranean species that have been introduced intentionally (as crops, forage, or ornamentals) or accidentally (in ballast, animal feed, clothing, animal droppings, fur, hooves, etc.). They are invasive weedy plants that are dependent on disturbed land for their establishment. The term "weed" is applied generally to plants that grow where humans do not want them. In other words, a weed is a relative thing: one person's flower garden is another's weed patch. However, specialists agree that weeds have certain characteristics shared by both native and introduced species. "Herbert Baker, a botanist at the University of California in Berkeley, once concocted a list of traits that the ideal weed would possess. No single weed has all of those traits or we would be ankle-deep in that species. Baker's list of traits for a successful weed includes fast growth rate, early maturity and reproduction, an abundant production of seeds, a prostrate habit, fragile stems, the capacity for wind- or self-pollination, tolerance of full sun, and seeds capable of long-term dormancy in soil. These traits are most easily combined in small, annual, herbaceous plants." Of the 5,867 plant species in California, approximately 1,416 species are endemic to California, and 1,023 others have been introduced and survive in the wild. Although some species occurring in anthropogenic communities are natives, most plants dominating these communities are non-native.

Pastoral communities have developed on lands, primarily grasslands, savannas, and oak woodlands, used for the grazing of domestic livestock - cows, sheep, and goats. Dominant species of these communities in Poly Canyon include Italian thistle (Carduus pycnocephalus) which is common in some places as a dense, spiny, impenetrable mass under coast live oaks. On the site that was once the Goldtrees' dairy, milk thistle (Silybum marianum) and perennial mustard (Hirschfeldia incana) dominate now. These communities occur adjacent to riparian, coastal live oak woodland, coastal scrub, chaparral, and rock outcrop communities. Pastoral communities are more fully discussed as non-native annual grasslands in the Grasslands section above. Agrestal communities develop on cultivated lands, not of concern in Poly Canyon. Ruderal communities occur along roads and trails. Plant growth in these communities is influenced not only by the usual climatic, geologic, and topographic factors, but also by other factors such as soil quality. The extreme compaction of soils that occurs at roadsides decreases the aeration of the soils, the penetration of water into the soils, and the diversity and number of soil-inhabiting creatures whose presence would counteract and even remedy the effects of soil compaction. Root development and penetration is more challenging under such conditions. Soil compaction also increases water runoff and erosion. With increased erosion, the organic layers of soil and nutrients are lost. Another factor that impacts ruderal species is pollution both by vehicle engines and pedestrian litter. The dust that cars, trucks, bicycles, and pedestrians kick up is another serious pollutant. It settles on leaves lowering the amount of sunlight received by the plants for photosynthesis. Also, it covers the pores on plant surfaces thus altering the processes of evapotranspiration.

A unique example of an anthropogenic community is found around the Poly Canyon landfill. There one can find the following assortment of plants: Canary Island date palm (Phoenix canariensis), tree tobacco (Nicotiana glauca), Eucalyptus spp., Pinus spp., pampas grass (Cortaderia jubata), cocklebur (Xanthium strumarium), poison hemlock (Conium maculatum), royal apricot (Prunus armeniaca), almond (Prunus dulcis), and peach (Prunus persica), to name a few. In that small area, all of the continents except Antarctica are represented by one or more of their native plants.

In Poly Canyon, ruderal communities are dominated primarily by:
Scarlet pimpernel (Anagallis arvensis, Primulaceae)
*Slender wild oat (Avena barbata, Poaceae)
*Wild oat (Avena fatua, Poaceae)
Black mustard (Brassica nigra, Brassicaceae)
*Ripgut grass (Bromus diabdrus, Poaceae)
Italian thistle (Carduus pycnocephalus, Asteraceae)
Pineapple weed, rayless chamomile (Chamomilla suaveolens, Asteraceae)
Bull thistle (Cirsium vulgare, Asteraceae)
Poison hemlock (Conium maculatum, Apiaceae)
*Storksbill filaree (Erodium botrys, Geraniaceae)
*Redstem filaree (Erodium cicutarium, Geraniaceae)
Fennel, sweet fennel (Foeniculum vulgare, Apiaceae)
Perennial mustard (Hirschfeldia incana, Brassicaceae)
*Foxtail (Hordeum murinum, Poaceae)
*Italian ryegrass (Lolium multiflorum, Poaceae)
Horehound (Marrubium vulgare, Lamiaceae)
California burclover (Medicago polymorpha, Fabaceae)
Sourclover (Melilotus indica, Fabaceae)
Tree tobacco (Nicotiana glauca, Solanaceae)
Bermuda buttercup (Oxalis pes-caprae, Oxalidaceae)
Bristly ox-tongue (Picris echioides, Asteraceae)
English plantain (Plantago lanceolata, Plantaginaceae)
Windmill pink (Silene gallica, Caryophyllaceae)
Milk thistle (Silybum marianum, Asteraceae)
Prickly sow-thistle (Sonchus asper, Asteraceae)
Common sow-thistle (Sonchus oleraceus, Asteraceae)
Chickweed (Stellaria media, Caryophyllaceae)

Descriptions of these plants follow.

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Scarlet pimpernel (Anagallis arvensis, Primulaceae) This is a 5- to 40-cm. (2- to 16-inch), low, spreading annual. Its square stems bear opposite, ovate leaves. The 7- to 11-mm. (1/4- to 1/2-inch) rotate flowers are salmon-colored and have a dark purple spot at the center. They bloom from February through October. The fruit is a spherical capsule. Scarlet pimpernel is native to Eurasia.

Anagallis is Greek meaning "to delight in again," probably because the flowers open each time they are touched by the sun. Arvensis means "of the fields."

Modern Chumash use this as a poultice for sores and to bathe for eczema and ringworm.

*Slender wild oat (Avena barbata, Poaceae)
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*Wild oat (Avena fatua, Poaceae)
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Black mustard (Brassica nigra, Brassicaceae) This is a 4- to 20-dm. (11/2- to 61/2-foot) plus, erect, branching annual. It has a basal rosette of pinnately lobed, finely toothed leaves, as well as similar leaves along the stems. Bright yellow, four-petalled flowers bloom at the branch tips from March through July. The fruit is a narrow, 1- to 2-cm. (1/2- to 1-inch) capsule with a round beak. Black mustard is native to Europe.

Brassica is Latin for "cabbage." Nigra means "black," referring to the color of the seeds.

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Italian thistle (Carduus pycnocephalus, Asteraceae) This hairy thistle is an annual. It has 2- to 20-dm. (1/2- to 61/2-foot) stems. It has alternate, spiny-toothed, pinnately lobed basal leaves with winged petioles. There are some similar, but smaller and sessile cauline leaves as well. Two to five heads of tubular florets are borne together in a cluster at the end of the main stem and branches. The tubular florets are pink-purple. The fruit is a tiny golden to brown achene with a pappus of barbed bristles. Italian thistle is native to the Mediterranean region.

Carduus is the ancient Latin name. Pycnocephalus means "thorny head."

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Pineapple weed, rayless chamomile (Chamomilla suaveolens, Asteraceae) This is a 10- to 30-cm. (4- to 12-inch) sweetly aromatic annual. Its leaves are twice to three times pinnately lobed. They are small, under 5 cm. (2 inches), and are bright green. The inflorescence is a 1-cm. (1/2-inch) diameter cone of miniscule yellow tubular florets. The fruit is a cylindric, ribbed achene.The plant is native to northeast Asia and northwest North America.

The derivation of the generic name is unknown. Suaveolens means "sweet-scented."

Manzanilla is the Spanish word for chamomile. Early Californians made an infusion of it to drink to alleviate stomach pains and nervousness; to induce perspiration; to reduce pain, cramps, colic; to suppress menstruation; for problems of the liver and in childbirth; to treat catarrh (either a common cold or an inflammation of the mucous membranes) and dysentery. A poultice of manzanilla was used to reduce inflammation. Now it is drunk as a tea to soothe nervousness and indigestion.

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Bull thistle (Cirsium vulgare, Asteraceae) This is a 3- to 20-dm. (2- to 5-foot) stout, hairy biennial. Its lanceolate, lobed leaves form a basal rosette. The leaf margins are spiny. Leaves along the stem are armed with spiny teeth and covered on the upper surface with short prickles. The inflorescence is a spiny-bracted head of purplish-red disk florets that bloom from March through September. The fruit is an achene with a pappus of plumose bristles. The plant is native to Eurasia.

Cirsium comes from the Greek kivsion, a kind of thistle. Vulgare means "common."

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Poison hemlock (Conium maculatum, Apiaceae) This is a 5- to 30-dm. (2- to 10-foot) branching biennial. It has smooth, stout stems that are green with purplish markings. The large leaves are finely dissected, feathery-like. The inflorescence is a compound umbel of white flowers that bloom from May through July. The fruits are oval schizocarps with wavy ribs. Poison hemlock is native to Eurasia. All parts of this plant are TOXIC if ingested.

Conium is the ancient Greek name for "hemlock." Maculatum means "spotted" and refers to the markings on the stem and petioles.

*Storksbill filaree (Erodium botrys, Geraniaceae)
click here for description

*Redstem filaree (Erodium cicutarium, Geraniaceae)
click here for description

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Fennel, sweet fennel (Foeniculum vulgare, Apiaceae) This is a 1- to 2-m. (3- to 6-foot) plus, stout, erect, glabrous perennial. The stems are green, streaked, and branching. The leaves are a deep, bright green and are finely dissected (feathery). They are very aromatic (smelling like licorice or anise). The inflorescence is a compound umbel of small yellow flowers that bloom from May through September. The fruits are oblong, ribbed schizocarps. Fennel is native to the Mediterranean region.

Foeniculum is Latin for "hay." Vulgare means "common."

The seeds, stems, and leaves of hinojo (in Spanish) are used as culinary herbs. The seeds and roots are infused as a digestive aid (carminative and appetizer).

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Perennial mustard (Hirschfeldia incana, Brassicaceae) This is a biennial or perennial. It has 2- to 10-dm. (8- to 40- inch) stems. Its pinnately lobed leaves are in a basal rosette flat on the ground, with some along the stems. The flowers have four pale yellow to white, clawed, obovate petals. The fruits are 1-11/2-cm. (1/2-to 3/4-inch), stout, club-like beaked capsules that are tightly appressed against the inflorescence axis. This mustard is native to the Mediterranean.

C. Hirschfeldt, 1742-1792, was a horticulturist. Incana means "gray."

Mostaza ("mustard" in Spanish) was introduced by Spaniards. Young greens and seeds are eaten.

*Foxtail (Hordeum murinum, Poaceae)
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*Italian ryegrass (Lolium multiflorum, Poaceae)
click here for description

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Horehound (Marrubium vulgare, Lamiaceae) This is a 1- to 6-dm. (1/2-to 2-foot) perennial that grows in mounds. Its squarish woolly stems bear gray-green, opposite, rounded, hairy leaves.The leaves have conspicuous veins and puckering. The inflorescence consists of dense clusters (whorls) of small white flowers. The tubular calyx has ten hooked teeth. Horehound blooms in spring and summer. Fruits are nutlets within a bur. Horehound is native to Europe.

Marrubium is Hebrew for "bitter juice." Vulgare means "common."

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California burclover (Medicago polymorpha, Fabaceae) This is a 1- to 4-dm. (4- to 16-inch) prostrate to ascending annual. It has glabrous stems. The pinnately compound leaves have three wedge-shaped leaflets. The inflorescence is a raceme of two to six yellow flowers. The fruit is a coiled, prickly bur (legume). This plant is native to Eurasia, the Mediterranean, and North Africa.

Medice is the Greek name for the related species alfalfa, Medicago sativa, which arrived to Greece via Medea. Polymorpha means "many forms."

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Sourclover, annual yellow sweet-clover (Melilotus indica, Fabaceae) This is a sweet-smelling annual. It has glabrous, spreading to erect 1- to 6-dm. (4- to 24-inch) stems. It has pinnately trifoliolate leaves with 1- to 21/2-cm. (1/2- to 1-inch), oblanceolate to wedge-shaped, sharply toothed leaflets. Its inflorescence is a slender and compact raceme about 1- to 2-cm (1/2- to 1-inch) long. Yellow flowers have 21/2-cm. (1-inch) petals. Fruits are much smaller indehiscent one-seeded legumes. Sourclover is found in open, disturbed areas. It is native to the Mediterranean.

Melilotus is Greek for "honey-Lotus." Indica means "of India."

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Tree tobacco (Nicotiana glauca, Solanaceae) Tree tobacco is a 2- to 6-m. (6- to 20-foot) shrub or small tree. It has ovate, smooth, glaucous, bluish-green leaves. Its 30- to 35-mm. (11/2- to 2-inch) yellow, tubular flowers bloom at branch tips year-round. The fruit is a capsule with many tiny black seeds. Tree tobacco is native to South America. All parts of the plant are TOXIC if ingested.

J. Nicot, 1530-1600, is said to have introduced tobacco to Europe. Glauca means "bluish-gray," referring to the powdery coating on this plant.

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Bermuda buttercup (Oxalis pes-caprae, Oxalidaceae) This perennial has stems that are mostly underground where it produces many small bulbs. The basal rosette of leaves is open. Leaves are compound and have three 31/2-cm. (11/2-inch) spotted, heart-shaped leaflets. The showy flowers have 21/2-cm. (1-inch) long yellow petals. They bloom from November through June. In California the plants fail to set seed, but spread by bulblets in disturbed soil. This is a native of South Africa.

Oxalis is Greek for "sour." Pes-caprae means "foot of the goat" and refers to the shape of the leaflets.

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Bristly ox-tongue (Picris echioides, Asteraceae) This annual or biennial has 3- to 8-dm. (1- to 11/2-foot) coarse, stout stems. Leaves are basal and cauline. They are oblong, entire, and coarsely toothed or shallowly lobed. The 2- to 4-cm. (1- to 11/2-inch) inflorescence is a dandelion-like head of yellow flowers surrounded by an outer ring of wide, prickly bracts and an inner ring of narrower, smooth bracts. The fruit is a brownish achene with a slender beak and a white pappus. Bristly ox-tongue is native to Europe.

Picris is Greek for "bitter." Echioides comes from echinus and means "hedgehog-/sea urchin-like."

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English plantain (Plantago lanceolata, Plantaginaceae) This perennial has a stout caudex and taproot. The 5- to 25-cm. (2- to 10-inch) leaves are all basal, mostly lanceolate, with several parallel veins and minutely toothed margins. The inflorescence is a cone-shaped, dense 2- to 8-cm. (1- to 3-inch) spike on a 20- to 80-dm. (8- to 32-inch) peduncle. The four-petaled flowers are inconspicuous. The fruit is a capsule. English plantain is native to Europe.

Plantago means "sole of foot/footprint." Lanceolata refers to the leaf shape.

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Windmill pink (Silene gallica, Caryophyllaceae) This is a 10- to 40-cm. (4- to 16-inch) hairy, sticky annual. The nodes of its stems have a swollen appearance. It has 1- to 31/2-cm. (1/2- to 11/2-inch), spade-shaped, opposite leaves. The showy flowers have five white-pink, ovate, clawed petals that are slightly turned, like the arms on a windmill. Blooms occur from February through May. The fruit is a capsule. Windmill pink is native to Europe.

Silene is probably named after the mythological Silenus (who was covered with foam, referring to the sticky secretions of many species in this genus). Gallica means "French."

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Milk thistle (Silybum marianum, Asteraceae) This is a 2- to 30-dm. (3/4- to 9-foot) annual. Its leaves are large, deeply lobed and coarsely toothed, and have wavy margins. The teeth and lobes are tipped with rigid spines. The leaves are shiny green with irregular bold white botches. Flowers are in 2- to 6-cm. (3/4- to 21/3-inch) spiny-bracted heads at branch tips. The flowers are rose-purple tubular florets that bloom from May through July. The fruit is an achene. This plant is native to the Mediterranean.

Silybum is Greek referring to thistle used for food. Marianum means "of Mary."

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Prickly sow-thistle (Sonchus asper, Asteraceae) This is a 1- to 12-dm. (4-inch to 4-foot) annual with milky sap. Some leaves are basal. Along the stem, there are also clasping, lobed leaves that have toothed blades. The teeth and the lobes are tipped with soft spines. The clasping lobes at the base of the leaf are spirally coiled. The inflorescence is a bristly-glandular dandelion-like head of yellow, ligulate flowers. The fruit is a flat, ribbed, beakless achene with a pappus of bristles. Prickly sow-thistle is native to Eurasia and Africa.

Sonchus is the ancient Greek name for this plant. Asperum means "rough, with minute points."

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Common sow-thistle (Sonchus oleraceus, Asteraceae) This is a 1- to 14-dm. (4-inch to 41/2-foot) annual with milky sap. It has basal and cauline leaves. The cauline leaves are clasping and have lobed blades whose terminal lobe may be shaped like an arrowhead. The clasping lobes at the base of the leaf are straight and sharply pointed. The inflorescence is a dandelion-like head of yellow, ligulate flowers. The fruit is a flat, ribbed, beakless achene with a pappus of white bristles. Common sow-thistle is native to Europe.

Sonchus is the ancient Greek name for this plant. Oleraceus means "aromatic."

Cardos, in Spanish, comes from cardar meaning to card or comb wool, a use of this plant.

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Chickweed (Stellaria media, Caryophyllaceae)This is a 7- to 50-cm. (23/4- to 20-inch) annual with weak, trailing, hairy stems. The leaves have 8- to 45-mm. (1/3- to 2-inch) ovate blades and are arranged opposite one another on the stem. The white flowers have 31/2-mm. (1/8-inch) petals that are two-parted at the tips. Chickweed may bloom all year in sheltered places, but mostly from February through April. The fruit is an ovate capsule. Chickweed is native to southwestern Europe.

Stellaria comes from the Latin stella, meaning star and referring to the shape of the flower. Media means "intermediate" or "middle-sized."