Taxus -Morphological ,anatomical and reproductive features &Economic importance

Taxus is a representative of conifers which is a prominent member in that group.It shows so many remarkable features in its morphology , Anatomy ,Reproduction and life cycle. It's economically importance is also great. This presentation is a overall description about Taxus.

1. TAXUS

2. MORPHOLO GY It is an evergreen tree attaining a height of 9-20 metres with a massive trunk . The stem is profusely branched and remains covered with a thin brown-coloured bark. Do not have dimorphi c branches The leaves are linear, small, only 2-3 cm. long and spirally arranged . eacvegetative sesses a single strong vein and recurved margins. The upper surface is dark green while the lower surface is pale or rusty red in colour.

3. The apex is sharply pointed mainly because of accumulation of silica. This sharply pointed apex may cause death of catties eating these leaves. Each leaf is shortly stalked. The stalk broadens into a flat persistent base which shows a slight twist. The scaly leaves present on the fertile shoot are opposite and decussate. Taxus possesses a long and well- developed tap-root. The roots are deep-feeders and highly branched.

4. Anat omy of Stem

5. It is irregular in outline and resembles Pinus in structure. T hickly cuticularised single-layered epidermis. parenchymatous cortex having some tannin-filled cells. It is followed by endodermis and sclerenchymatous pericycle. The young stem shows a ring of conjoint, collateral, open and endarch vascular bundles enclosing a distinct pith in the centre. The protoxylem consists of spiral tracheids, and the phloem contains sieve cells with sieve plates and phloem parenchyma. Companion cells are absent.

6. secondary g rowth of the stem

7. The cambium cuts secondary phloem towards outer side and secondary xylem towards inner side . The secondary wood is devoid of resin canals and wood parenchyma. Its tracheids show uniseriate bordered pits only on their radial walls.
The tracheids also show spiral thickenings Th e wood is strong and dense. Due to the presence of tertiary spirals the wood is elastic in nature. Phellogen may develop in the older stems showing extrastelar secondary’ growth.

8. Anat omy of leaf

9. The leaf is dorsiventral. It shows xerophytic characters. Upper and lower epidermal cells are rectangular in shape and thickly circularized. The cuticle is comparatively thin on the lower surface. The stomata are of sunken type and restricted only to the lower epidermis . The mesophyll is differentiated into palisade and spongy-parenchyma. The palisade is generally two-layered.

10. Only one vascular bundle is present in the mid-rib region. Enclosed by a distinct endodermal layer or bundle sheath the collateral vascular bundle contains phloem towards the lower side and xylem towards the upper side. Transfusion tissue is present on both the sides of the vascular bundle. Resin canals are generally absent. The xerophytic characters of the leaf include the presence of thick cuticle, sunken stomata, transfusion tissue and differentiation of mesophyll into palisade and spongy parenchyma.

11. Reproduction in Taxus Taxus is usually dioecious, but occasionally monoecious trees are also reported vegetative reproduct ion is absent

12. Male strobil us or male flower The ‘male flowers’ or ‘male strobili’ are usually yellowish in colour and develop in the axil of foliage leaves . Each strobilus contains a number of overlapping sterile bracts Some of the bracts towards the tip of the strobilus are replaced by stamens or micro-sporangiophores. Each stamen is shortly-stalked any has a peltate disc bearing 4-8 pendant microsporangia

13. Each stamen is shortly-stalked any has a peltate disc bearing 4-8 pendant microsporangia. The microsporangia surround the stalk completely The microsporangia in the young male strobilus are compactly arranged but at maturity they get loosened and undergo dehiscence. The presence of peltate micro-sporangiophores is one of the most remarkable features of Taxus.

14. Female strobilus or Female cone The female strobili in Taxus are so highly reduced that they hardly appear as cones or strobili. They arise in the axils of leaves early in the season and mature in the next season.

15. Each female reproductive organ consists of a short primary axis having scaly leaves or bracts arranged in opposite decussate manner A short secondary axis develops from the axil of upper three scaly leaves. This secondary axis bears a few pairs of scaly leaves and a terminal ovule . According to Dupler (1920) the primary axis functions only as a vegetative branch of limited growth bearing the reproductive secondary axis.

16. Struc ture of Ovule The ovule is orthotropous and sessile . A single thick integument is present. Integument is free from the nucellus right up to its base forming egument is differentiated into outer fleshy, middle stony and inner fleshy layers

17. A ring-like outgrowth develops from the base of the integument. It surrounds the entire ovule. It is called ‘aril’ or ‘cupule’ . Aril is green and saucer-shaped when young but at maturity it is red and cup-shaped. Pollen chamber and nucellar beak are absent in Taxus. The apex of the female gametophyte changes into a flask-shaped structure called tent-pole. The tent-pole disappears in the later stages.

18. Generally, up to 10 archegonia develop in the female gametophyte but sometimes as many as 25 archegonia may appear.

19. Seeds Taxus seeds are covered by a three-layered seed coat. The outermost layer is thin, brown and detaches soon. The middle layer is hard and stony while the innermost layer is fleshy. The mature seeds are covered by a red coloured aril. The aril serves to attract birds and help in dissemination.

20. Econ omic Importance widely c u l t i v a t e d as an ornamental plant . T he timber of Taxus baccata and some other species is oily and heaviest of the soft woods. It is quite durable and used for making decorative veneers, turnery, flowers and posts. Several other types of decorative pieces are also made from its wood.

21. Due to the presence of a toxic alkaloid (taxine) in the leaves, shoots and seeds, the entire plant of Taxus baccata is considered poisonous and also used in some countries as a fish poison. Its leaves also contain traces of ephedrine, and, therefore, used in bronchitis, asthama and epilepsy. Seeds of T. baccata are used as sedative.

22. Taxol is a drug obtain ed fr om the bark of taxus tree .Taxol is used for the treatment of breast, ovarian, lung, bladder, prostate, melanoma, esophageal, as well as other types of solid tumor cancers.

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