Flora

Knowledge about the flora of Yemen is scattered, being found in more than 250 publications from 1775 up to the present date. However, no comprehensive work has yet been done on the flora of Yemen. Long periods of drought have prevented botanists from collecting annuals and short-lived species.

When analysing the available information in the literature and our fieldwork, the following facts are found:

1. Number of species: 2000 belonging to 700 genera and 125 families

2. The dominant families are:

These form 50% of the flora

3. The dominant genera are:

4. On Socotra there are about 500 species belonging to 146 genera. Nineteen families are monocotyledonous.

5. The life forms of the Yemeni flora consist of the following:

• Herbs and perennials 63%
• Small shrubs 23%
• Large shrubs and trees 8%
• Succulents 6%
  

Endemism in the flora of Yemen

The flora of Yemen is the least explored in Arabia. Therefore a lot of work still has to be done and many plants described. For example, in the last two years (1994 and 1995) 12 new species were described. These are listed below:
1. Cucumis canoxyii Thulin & Gifri (1994)
2. Euphorbia applanata Thulin & Gifri (1995)
3. Ochradenus gifrii Thulin (1995)
4. Campalanthus antonii Thulin (1995)
5. Echidnopsis globosa Thulin & Hetjerson (1995)
6. Diplotaxis kohlaanensis A. Miller & J. Nyberg (1994)
7. Phragmanthera austroarabica A. Miller & J. Nyberg (1994)
8. Commicarpus adenensis A. Miller (1994)
9. Forsskaolea griersonii A. Miller & J. Nyberg (1994)
10. Acacia yemense L. Boulos (1995)
11. Acacia johnwoodii L. Boulos (1995)
12. Kraussia socotrana Bridson (1995)

These species are all considered as being endemic to the region. According to the literature on the flora of Yemen about 12% of the Yemeni flora is endemic. On the island of Socotra, however, endemism is in the region of 30%. Eleven genera are endemic to Socotra and four to the mainland. Of these endemics, Saltia and Centaurothamnus are also found in Saudi Arabia, Xerotia in Oman and Isoleucas is found at Ras Fartak in South Yemen.

In the study of the flora of any country endemism is of central significance. Endemism is also important in establishing priorities for conservation. This paper therefore highlights the centres of endemism in Yemen.

1. Hujariyah. This is a mountainous area south of Taiz. After Socotra, it is the richest survey square with 99 endemics (Miller et al. 1991). There are eight endemics that are restricted to it including Kickxia woodii D. A. Sutton, Crotalaria squamigera Deflers, Centaurea yemense Wagenitz and Blepharispermum yemense Deflers.
2. Ibb. These western escarpment mountains are the habitat of many endemics. The taxa occur mainly around Sumara Pass at a height of over 2800 m. Among its endemics are Kniphofia sumarae Deflers and Helichrysum arwae J. R. I. Wood.
3. Hadramout Jol. This is the top of the plateau. It is formed of limestone and is intersected by many wadis. A part of it known as Kar Sieban is often covered with mist. Endemics such as Anogeissus bentii Baker, Schweinfurthia latifolia Oliv., Cucumus canoxyii Thulin & Gifri, Euphorbia applanata Thulin & Gifri and Echidnopsis globosa Thulin & Hetjerson, occur in this region.
4. Jabal Areys. A frequently mist-covered volcanic massif lying 150 km east of Aden on the southern coast of Yemen. A number of endemics are recorded such as: Cystostemon kissenioides (Deflers) A. Miller & Riedl, Salvia areysiana Deflers, Kleinia deflersii (O. Schwarz) P. Halliday.
5. Jabal Fartak or Ras Fartak. This is the mountainous part of the Al-Mahra region on the coast. It receives a lot of dew and for that reason a number of endemics occur in the area: the genus Isoleucus, Campylanthus antonii Thulin and Ochradenus gifrii Thulin.

To conclude, the richest region in the Arabian Peninsula for endemics is the mainland of Yemen, with 149 species (11.5% of the flora of Yemen). Socotra stands in a class of its own with 240 species (30% of the flora of Yemen). Floristically, Hujariyah to the south of Taiz is perhaps the richest area in Arabia. However, the flora of Yemen has been inadequately studied and even the endemics although recorded are poorly known.