Instead of seta in capsule of Sphagnum the structure present is
A. Columella
B. Pseudopodium
C. Haustra
D. Root

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Hint:-Sphagnum which belongs to the group bryophytes of kingdom Plantae. So for sexual reproduction, there are so many types of spores. Seta is one of the sporophytes which represents the spore of bryophytes, but in case of sphagnum, the seta is absent and other spores present.

Complete answer:The Sporophyte:
The sporophyte generation of bryophytes or mosses is completely dependent on the never makes independent contact with any substrate. So we treat it as an anatomical extension of the gametophyte conditions. A generalized bryophyte sporophyte can be considered as having three parts: a "foot" which connects the embryo to the gametophyte to extract nutrients, a seta which lifts the mature sporophyte clear of the gametophyte body, and a terminal sporangium capsule.
(I) generally, the sporophyte is surrounded by the epigonium, which is a protective coat supplied by the gametophyte. When the sporophyte grows, it elongates and grows to form fracturing the structure teemed as a calyptra. The last remnants from a loosely pointed and apically dunce cap, the calyptra, a ring around the base, termed as a vaginula. At the same time (approximately - the timing is quite variable) three other things are going on. (II) the inner sporophyte capsule (a/k/a urnorangium) is developing and hardening. (III) itself clear of the mother-ship on a long extension tube, termed as the seta. (IV) Inside the sporophyte, cells on the surface of a central columella (think of it as a little internal shoot) are undergoing meiotic divisions to create haploid spores. The small spaces where this is going on are called loculi. Loculus may be translated to mean, oddly enough, "small space." Perhaps, fortunately, people tend to avoid Latin these days and refer to it as a location.
Later, the calyptra dries up completely and falls off, and the capsule is exposed, with the end sealed by a small operculum. Eventually, this, too, is lost. Many more derived mosses have another control on spore dispersal i.e. a peristome with peristome teeth arranged around an annulus. The teeth are quite diagnostic of the species and are much sought after by species-level taxonomists for this reason. The teeth are so constructed that they bend outward as they dry out, causing the opening to widen and release the spores. Note that this entire system is designed to promote spore dispersal is relatively sustained dry weather and moderate winds. That seems an odd sort of requirement for a plant that requires flowing water for sexual reproduction.
Bear in mind that this describes sporophyte development in an imaginary "typical" moss. As we keep saying, there is a great deal of variation. Sphagnum, for example, has no seta. The sporophyte is raised by the pseudopodium, a structure produced by the parent gametophyte in case of sphagnum and some basal mosses.

So B is the correct option.

Note:- Eventually the sporophytes of bryophytes or mosses are to teemed as seta but some exceptions are present so we have to remember it because this is just an example as like in case of sphagnum it is called as pseudopodium. Also another name of sphagnum is known as peat moss.

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