Pteridophytes

In $Equisetum$ (a pteridophyte), sporophylls are aggregated to form compact structures called strobili or cones.

In heterosporous pteridophytes such as Selaginella and Salvinia the female gametophyte is retained on the parent sporophyte for a variable period, and the zygote develops into a young embryo there.
This event is a precursor to the seed habit, so the origin of the seed habit can be traced in pteridophytes.
Protonema and leafy stages are found in mosses, the gymnosperm female gametophyte is not free-living, and antheridiophores and archegoniophores occur in liverworts such as Marchantia.

$Selaginella$ and $Salvinia$ are heterosporous pteridophytes: they produce two kinds of spores, small microspores and large megaspores.
The megaspores germinate into female gametophytes, which are retained on the parent sporophyte for variable periods.
The development of the zygote into a young embryo takes place within this female gametophyte.
NCERT describes this event as a precursor to the seed habit and an important step in evolution.
There is no seed coat or endosperm in these plants, the female gametophyte is not shed free like a seed, and it does bear archegonia.
Hence the reason is that the embryo develops in the female gametophyte which is retained on the parent sporophyte.

Cryptogams are plants that do not produce seeds (algae, bryophytes and pteridophytes).
Pteridophytes are the first terrestrial plants to possess vascular tissues, xylem and phloem, but they reproduce by spores; they are therefore called vascular cryptogams.
$Equisetum$ (horsetail) is a pteridophyte.
$Cedrus$ and $Ginkgo$ are gymnosperms, which are seed plants (phanerogams).
$Marchantia$ is a liverwort (bryophyte), a non-vascular cryptogam.
Hence the vascular cryptogam is $Equisetum$.

Heterospory is the production of two kinds of spores, small microspores and large megaspores, as in $Selaginella$ and $Salvinia$.
The megaspores germinate into female gametophytes that are retained on the parent sporophyte for variable periods.
The development of the zygote into a young embryo takes place within the female gametophyte.
This retention and protected development is a precursor to the seed habit and is considered an important step in evolution.
A free-living gametophyte or a haplontic life cycle works against, not towards, the seed habit.
Hence heterospory is important in the development of the seed habit.

Most pteridophytes produce only one kind of spores and are called homosporous.
A few genera produce two kinds of spores, small microspores and large macrospores (megaspores); they are called heterosporous.
Selaginella and Salvinia are the common examples of heterosporous pteridophytes.
The microspores and megaspores germinate to give male and female gametophytes respectively, and the female gametophyte is retained on the parent sporophyte for some time.
This event is considered a precursor to the seed habit, an important step in evolution.
Adiantum, Equisetum and Dryopteris are homosporous.
So the heterosporous plant is Salvinia.

Vascular cryptogams are the pteridophytes. Their gametophyte is a small, free-living, mostly photosynthetic thallus called the prothallus.
In most ferns the prothallus is monoecious; it bears both antheridia (male sex organs) and archegonia (female sex organs).
When the antherozoids and the eggs of the same prothallus mature at different times (usually the antheridia mature first, a condition called protandry), the antherozoids cannot fertilise the eggs of the same prothallus.
The eggs are then fertilised by antherozoids coming from another prothallus.
So self-fertilisation is prevented and cross-fertilisation is promoted, which brings about genetic variation.
It does not cause sterility or apomixis, and it does change the pattern of fertilisation.
Hence the result is that self-fertilization is prevented.