Welwitchia Notes

Welwitchia 

SYSTEMATIC POSITION

GROUP                                 Spermatophyta

Sub-Group                      Gymnospermae                                                 

Class                                      Gnetales

Order                                    Gnetopsida

Family                                  Welwitschioceae

Genus                                   Welwitschia

Welwitschia is a monotypic gymnosperm genus, comprising solely the distinctive Welwitschia mirabilis. The plant is commonly known simply as welwitschia in English, but the name tree tumbo is also used. It is called kharos or khurub in Nama, tweeblaarkanniedood in Afrikaans, nyanka in Damara, and onyanga in Herero. Welwitschia is the only genus of the family Welwitschiaceae and order Welwitschiales, in the division Gnetophyta. Welwitschia mirabilis is found to be endemic in the deserts of Namibia (Namib Desert) and Angola.

Distribution:

            The genus Welwitschia (named after Dr. Welwitsch), who discovered it in (1860) includes only a species W.mirabilis which occurs in the Kalahari desert of Western South Africa. The specific name is very appropriate because the adult sporophyte is one of the most remarkable plants known to science. Since only a few thousand plants are reported to be left now in Africa, they are protected by law which carries a penalty of a fine and a prison term for anyone who destroys one of these botanical curiosities.

EXTERNAL CHARACTERS

            The plant (sporophyte) has been described as a gigantic wooden radish because it consists of a short axis, shaped like a radish, turnip or sugar beet, from whose flattened crown are borne only two strap-shaped leaves which continue growing for at least a century, wearing and tearing at the tip, but being renewed continually by a meristem at the leaf base. In most of the desert areas, where Welwitschia grows, the rainfall is scanty;  the exceptionally  long tap-root characteristic of old plants may be an important factor in its survival in such unhospitable areas. Possibly as suggested by Rodin, prior to the development of a tap-root, young plant may utilize condensed moisture of dew and frost.

REPRODUCTIVE ORGANS

            The plants are dioecious and bear cone shaped strobili at the edge of the crown of the stem.

STAMINATE (MALE) STROBILUS

            In the staminate strobilus, the “flowers” are borne in the axis of the bracts. They differ considerably from those of Gnetum and Epedra.

            The male “flower” consists of a circle of six stamens, united at the base (monoadelphous), each bearing at its tip three sporangia. Within the circle of stamens is a single abortive ovule with its long, spirally-coiled micropylar tube ending in a broad, flaring tip.

OVULATE (FEMALE) STROBILUS

            The ovulate strobilus resembles the staminate strobilus in its general make-up. The “female flower” consists of an ovule with integuments. It is surrounded by bracts resembling perianth. A set of rudimentary “stamens” appears outside the ovule.