Clandestine stipa

Clandestine stipa, known as picudo grass, esparto grass or hack b>, is a species of grass in the Poaceae family.

Description

It is a perennial, bushy plant, 30 to 80 cm tall. Stems with one or three glabrous or pubescent nodes, and glabrous internodes. Leaf with sheath 8 to 20 cm long, smooth and glabrous, light green or yellowish green, longer than the internodes, open to the base with a hyaline margin and scalloped at least in the area near the neck, where it is open at the base. "V" shape and sometimes hairy; ligule formed by bristles 2-3 mm long, whitish; linear blade 2-6 DM long and 2-2.5 mm wide, revolute margin, making it 1 mm wide and wire-like in appearance; soft when it is tender, hard and sharp when it is ripe; upper surface scabrous, lower surface smooth. Inflorescence: panicle 15-35 cm long; pendulous, its secondary axes flexuous. Unifloscular spikelet that is disarticulated above the glumes, the articulation is oblique and leaves a bearded neck on the floret; glumes equal or subequal, 4-7 mm long, hyaline edges, greenish or purplish color that remains on the inflorescence after the caryopsis is detached; floret as long as or less than the glumes, purplish, hairy, with an awn 12-18 mm long, geniculate and tortuous. Fruit present in the form of a dispersed caryopsis and wrapped in a floret formed by a palea and a frisky lemma, easily detachable from the caryopse. The lemma shows a very long, twisted and fragile awn, the floret is greenish or purple.

Caryopsis ovate or almost ovate in outline, clavate in shape, 2.1 to 2.7 mm long and 0.1 to 1.2 mm wide, with an almost circular cross section, although sometimes it appears as a slightly rhombus irregular; dorsal side with a rib generally slightly forked or broadened towards lower half of fruit; the ventral and lateral sides generally also have a rib in the middle part, but it is not bifurcated and is often inconspicuous. Fruit apex with a short extension, fruit base acute with the insertion scar on one side; almost smooth surface or with small, sparsely prominent wart, yellowish-green to yellowish-brown in color, with a purplish apical spot occasionally present.

It has an elongated torn coleoptile, often 3-15 mm, hyaline, with two conspicuous converging veins, the same size as the sheath of the first leaf. First leaf with sheath the same size as the coleoptile, ligule formed by whitish bristles, linear blade 7-25 mm long, frequently incurved when dry, 0.5 mm long, glabrous. Second leaf also similar, blade 8-37 mm long and 0.5-1 mm wide, linear, grooved in section, second apex, with conspicuous veins. There is no description of the basal and axillary inflorescences and fruits.

Importance

Plant present in alfalfa fields three years old or older where it can be very abundant and difficult to control. In addition to ruderal and pioneer, it is found on the banks of canals. This species is associated with alfalfa fields subjected to cuts, the step appears on the edges of the beds and watering cans, areas in which the cut is not so low, which allows the formation of tillers and the production of basal seeds.

The production of basal or cleistogamous seeds has been known as a phenomenon of somatic polymorphism. The aerial fruits are smaller and more numerous than the underground ones and are dispersed by the wind; while the underground fruits never leave the dead mother plant, germinating and emerging through its tissues, then; the aerial fruits serve for the dispersal of the plant towards new habitats, while the underground fruits are adapted to increase the survival of the species in the already occupied habitat. The phenomenon of cleistogamy is not rare among different families and species, Stipa leucotricha is described as a species that produces abundant basal cleistogamous spikelets, under certain environmental conditions, in addition to low soil moisture. as a condition for the induction of cleistogamous flower production in G. micranta.

Seed germination

The seed is the unit of sexual reproduction par excellence in higher plants, and is in charge of propagating the species and dispersing it spatially and temporally. According to this, the seeds of plants, and of course weeds, have the ability to remain in a state of minimal activity for long periods, germination from the physiological point of view is the process that begins with the supply of water to the seed and ends when the growth of the seedling begins, this moment being more commonly considered when the radical emerges through the integument.

Stages in seed germination

There are three fundamental phases in the seed germination process: hydration or imbibition phase, which consists of the absorption of water by the seed tissues and a considerable increase in its respiration rate; the germination phase, in which profound metabolic changes occur, in this phase the absorption of water is considerably reduced, and the growth phase, in which evident morphological changes occur, such as the elongation of the radical, and is characterized by the constant increase in water absorption and respiration.

Dormancy or lethargy of the seed

Even when the environmental conditions are suitable for seed germination, many of them do not, even if they remain viable. Seed non-germination is also known as dormancy or lethargy (Zimdahl, 1993), and is linked to intrinsic causes of the seeds or fruits, but also to environmental effects.

Environmental causes that induce latency

Oxygen

The balance in the concentration of O2 and CO2 in the soil atmosphere is important in the germination of weeds. In compact or poorly drained soils, O2 contents are frequently lower than those necessary for seed germination. One of the reasons most seeds germinate near the soil surface is the higher concentration of oxygen.

Temperature

There are temperatures below or above which a seed will not germinate. The optimum temperature for seed germination depends on the species. Very low or very high temperatures consequently induce lethargy.

Ecological meaning of dormancy or torpor

Dormancy is the main cause of weed seed survival in the soil, thus it is the reason for prolonged infestation of crops by weeds. In agricultural soils, the seed reserve can be important, and up to 120 million seeds (or more) per m³ can be found in the course of the following crop year, generally more than 10% of this potential seedbed appears. This variability of germination responses leads to a heterogeneity of the latent states of the seeds that remain on the surface of the soil or buried, making it difficult to predict infestations in crops.

The permanence on the surface or inside of the seed viable and capable of germinating is generally caused by the inhibition of germination and secondary dormancy, until favorable conditions appear for the establishment of its seedlings.

Scarification

This is the most common method used to increase the germination of seeds with a hard coat. Scarification techniques can partially remove the integument or just alter it for germination to take place. There are essentially two types: mechanical and chemical scarification.

Mechanical scarification can be done by means of an electric scarifier or with any abrasive that cuts, perforates or scrapes the integument. The chemical scarification method is carried out by immersing the seeds in concentrated sulfuric acid, for a time which depends on each species.

Abiotic factors that affect plants

Some factors that affect seed production are:

• Delaying growth in spring.
• Decrease in size and number of leaves.
• Shortness of floral stems, and of late appearance.
• Seed maturity, limited production and low viability of harvested seed.
• Low germination and little refill of the plants in the next spring.

Description

All Stipa can be recognized by having very long awns, in the case of Stipa capensis the awns are between 5 and 10 cm, and when mature they are rolled up between them becoming completely entangled (this species has also been called Stipa retorta). It is a grass that forms relatively dense meadows, but never rises much above the ground; It is always found in fairly dry and open areas.

Taxonomy

Stipa clandestina was described by Eduard Hackel and published in Repertorium Specierum Novarum Regni Vegetabilis 8: 516. 1910.

Etymology

Stipa: generic name derived from the Greek stupe (tow, tow) or stuppeion (fiber), alluding to the feathery awns of the Eurasian species, or (more likely) to the fiber obtained from esparto grasses.

clandestine: Latin epithet meaning "hidden".

Sinonimia

• Achnatherum clandestinum (Hack.) Barkworth
• Amelichloa clandestine (Hack.) Arriaga & Barkworth