Gymnosperms are seed plants that have evolved cones to carry their
reproductive structures.
LEARNING OBJECTIVE [ edit ]
Discuss the type of seeds produced by gymnosperms
KEY POINTS [ edit ]
Gymnosperms produce both male and female cones, each making the gametes needed for
fertilization; this makes themheterosporous.
Megaspores made in cones develop into the ovules of gymnosperms, while pollen grains develop
from cones that produce microspores.
Conifer sperm do not have flagella but rather move by way of a pollen tube once in contact with
the ovule.
TERMS [ edit ]
heterosporous
producing both male and female gametophytes
sporophyll
the equivalent to a leaf in ferns and mosses that bears thesporangia
ovule
the structure in a plant that develops into a seed after fertilization; the megasporangium of a seed
plant with its enclosing integuments
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Characteristics of Gymnosperms
Gymnosperms are seed plants adapted to life on land; thus, they are autotrophic,
photosynthetic organisms that tend to
conserve water. They have a vascular
system (used for the transportation of
water and nutrients) that includes
roots,xylem, and phloem. The name
gymnosperm means "naked seed," which
is the major distinguishing factor between
gymnosperms and angiosperms, the two
distinct subgroups of seed plants. This
term comes from the fact that the ovules
and seeds of gymnosperms develop on the
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scales of cones rather than in enclosed chambers called ovaries.
Gymnosperms are older than angiosperms on the evolutionary scale. They are found far
earlier in the fossil record than angiosperms. As will be discussed in subsequent sections, the
various environmental adaptationsgymnosperms have represent a step on the path to the
most successful (diversity­wise) clade (monophyletic branch).
Gymnosperm Reproduction and Seeds
Gymnosperms are sporophytes (a plant with two copies of itsgenetic material, capable of
producing spores). Theirsporangia (receptacle in which asexual spores are formed) are found
on sporophylls, plated scale­like structures that together make up cones. The female
gametophyte develops from the haploid (meaning one set of genetic material) spores that are
contained within the sporangia. Like all seed plants, gymnosperms are heterosporous: both
sexes of gametophytes develop from different types of spores produced by separate cones.
One type of cone is the small pollen cone, which produces microspores that subsequently
develop into pollen grains . The other type of cones, the larger "ovulate" cones, make
megaspores that develop into female gametophytes called ovules . Incredibly, this whole
sexual process can take three years: from the production of the two sexes of gametophytes, to
bringing the gametophytes together in the process of pollination, and finally to forming
mature seeds from fertilized ovules. After this process is completed, the individual
sporophylls separate (the cone breaks apart) and float in the wind to a habitable place. This
is concluded withgermination and the formation of a seedling. Conifers have sperm that do
not have flagella, but instead are conveyed to the egg via a pollen tube. It is important to note
that the seeds of gymnosperms are not enclosed in their final state upon the cone.
Female cone of Tamarack pine
The female cone of Pinus tontorta, the Tamarack Pine, showing the rough scales. This is the cone that
produces ovules.
Male cone of Tamarack pine
The male cone of Pinus tontorta, the Tamarack pine, showing the close proximity of the scales. This is the
cone that produces pollen.