Tragopogon
(Salsify)
Tragopogon is a genus of Asteraceae usually described as biennials or short-lived perennials. They are really monocarpic perennials, living for 2 or more years until they flower. After flowering the plant senesces and dies. The plant shown here is Tragopogon porrifolius (Salsify or Common Salsify) subsepcies porrifolius (= var. sativus). This plant may reach 1 m in height and has a hairless, upright stem.
Tragopogon plants are also known as 'Jack-go-to-bed-at-noon' due to an interesting behaviour: the flowers open early each morning (they are one of the first day plants to open between 3:00 and 5:00 am) and face the Sun, tracking it across the sky, and closing around noon, assuming an upright posture.
Above and below: Tragopogon porrifolius facing the Sun. A population was growing along the banks of a tidal river here and all were pointing straight towards the Sun. The linear leaves are dilated at the base and narrow gradually towards the apex (in T. pratensis they taper suddenly).
As members of the Asteraceae, the 'flower' is actually a compound or composite flower-head (capitulum) made up of a number of individual flowers or florets arrayed together. The long petal-tubes of the outermost florets form the elongated ray-like ligules. Eight (usually) equal green bracts, the phyllaries, which are united at their bases and form the cup of the capitulum.
Below: Tragopogon porrifolius in the afternoon, having closed and having tracked the Sun until noon they now assume an erect posture. This fascinating behavior of tracking the Sun presumably helps the plants attract pollinating bees, by keeping the flowers well lit and hence visually eye-catching and possibly also by warming the flowers in the sun. Warm platforms may serve as sunning spots for early morning insects to warm their bodies and warmth may also evaporate volatiles that create an attractive aroma. Typical of Asteraceae there is a ring nectary on top of the ovary in each floret. Tragopogon porrifolius is frequently visited by a variety of bees, such as the small bee Andrena thoracica (Cliff Mining Bee).
When closed, T. porrifolius can still be distinguished from T. pratensis because in the former the stem (technically peduncle or inflorescence stalk) thickens considerably just beneath the capitulum (anthode), as shown here. What is the advantage of closing at mid-day? Clearly Tragopogon has evolved to take advantage of early morning pollinators and then closes its flowers around noon, perhaps to protect the nectar from other pollinators or nectar thieves. Bees presumably learn that this source of nectar is available in the morning and gather there at the right time. Indeed, Tragopogon is one of the first day flowers to open, opening as early as 3:00 am.This perhaps help to avoid competition for pollinators from other plants.(In contrast, dandelion, Taraxacum officinale opens from about 10:00 am in the morning until 10:00 am at night).
The dry fruit, produced by each pollinated floret contains a single seed and the fruit skin (pericarp) is contoured tightly around the seed; such a fruit is called an achene (or more strictly cypsela depending what classification of fruit one uses, personally I don't generally distinguish between an achene and a cypsela).
Each achene is crowned by a plume of hairs to form a pappus, which is borne on a beak-like extension of the achene. The fruiting head forms a globe of feathery fruit, resembling those in Dandelion, but larger. This opens in dry conditions for fruit dispersal by the wind. The pappus forms a parachute that creates drag to slow the descent of the achene and hence prolong the time it spends airborne, so maximizing dispersal by the wind. The pappus is best studied in Tragopogon pratensis. The primary hairs or fibers (consisting of a chain of several cells) are about 18 mm in length, each tipped in a spine, and give off secondary fibers or barbs, each consisting of a single elongated cell. The secondary fibers interlock with those on neighboring primary hairs to form a fine and complexly woven mesh.
Studies show that the porosity of this pappus chute is optimized to maximize drag 9in part by reducing the weight of the chute) - see the study by Casseau et al. 2015 (PLOS ONE, DOI:10.1371/journal.pone.0125040, Morphological and aerodynamic considerations regarding the plumed seeds of Tragopon pratensis and their implications for seed dispersal).
Despite the achenes being much heavier than those of dandelion (Taraxacum officinale) both achieve similar drag and rates of descent. (The achenes of Tragopogon pratensis weigh about 11 mg (4 - 17 mg) whereas those of Taraxacum officinale weigh about 0.65 mg). Interestingly the pappus opens and closes according to humidity in the first few days, opening when dry when conditions favor dispersal (before, presumably, remaining open).
At least in Tragopogon pratensis and Tragopogon dubius, there are two achene types, or more specifically, a gradation from smaller and lighter colored achenes in the center of the capitulum to heavier and darker seeds at the periphery. This might reflect the fact that developmentally there is generally more space to develop larger and 'more mature' achenes towards the periphery, where the florets in Asteraceae ripen first. However, it may also be adaptive. Sometimes the more central achenes are generally smoother in texture, at least in T. pratensis. Both achene types, however, germinate equally as well, but the larger achenes (at least in T. dubius) give rise to larger seedlings. Tragopogon produces several capitula and in T. pratensis 100 to 850 seeds per plant. In T. pratensis it has been found that about 10% of the achenes germinate in the same summer, the rest germinating the following winter/spring.
The long parsnip-like taproot of Tragopogon porrifolius is edible and the plant has been grown for food. It has been said that it exceeds the carrot and parsnip in flavor, and like parsnip roots it is considered best after an autumn frost. The green parts are also edible and said to be sweet and have been used in soups and salads. (Personally I prefer to leave them for others to enjoy their visual beauty when found growing wild). Generally considered an alien in the British Isles, it is possibly native in southern England.
All florets of Tragopogon are ligulate: that is their corolla tubes are extended into strap-like 'petals', each of which is really 5 fused petals (as is apparent when looking at their tips). The outer florets open first and unopened inner florets resemble disc florets. (In many Asteraceae disk florets covering the main central disk of the capitulum have tube or bell-shaped petal-tubes whilst marginal florets are often ligulate or ray-like, though all flowers may be disk-type or ligulate in some Asteraceae).
Below: Tragopogon porrifolius ssp. australis (= var. parviflorus). In this subspecies the outer florets are only about half the length of the phyllaries (basically the outer ligules are absent). (Each achene also narrows gradually to form a beak in this subspecies whereas they narrow abruptly to form a beak in ssp. porrifolius, with the beak bearing the pappus.)
Tragopogon pratensis (Meadow Salsify, Goat's-beard) is another well known species with yellow florets (though there may be purple on the underside of the ligules which can confuse determination when the flowers are closed).
In North America, Tragopogon porrifolius and Tragopogon pratensis form a breeding complex with Tragopogon dubius. These 3 species are all diploids (2n = 12) but hybridize to form the (allo)tetraploids (4d = 2n = 24) Tragopogon mirus and Tragopogon miscellus.
This is one of many demonstrable examples of speciation - the formation of a new species - with T. miscellus appearing in N. America around 1930. The ability of flowering plants to so readily hybridize (and then adapt by natural selection) partly accounts for the impressive diversification of flowering plants (angiosperms) in the course of evolution.
The seed-heads of Tragopon porrifolius. These no longer close at noon but do appear to close in damp weather (as do Dandelion 'clocks') at least when young. Closure results from movements of the sepals and each pappus. This optimizes dispersal in dry weather and protects the pappus from damage by rainfall.
The seed-heads of Tragopogon are much larger than those of the Dandelion (Taraxacum officinale) and the different architecture of the achene and pappus give them a very distinct appearance.
The long beak on each fruit, which bears the pappus, can be clearly seen.