Persea americana, "avocado"  



Fig. 1: Flower of P. americana.
Species: Persea americana Mill.

Family: Lauraceae (see also Use below)

Related Families: Order Magnoliales1,2,3, or LauralesTree of Life

Distribution: Native to Central America, cultivated in tropical and sub-tropical climates around the world.

The inflorescences in the family Lauraceae are usually determinate, arising from axillary meristems4. In Persea americana they are mostly lateral on a continuing vegetative shoot . The inflorescences form determinate lateral panicles5, which develop acropetally, producing tertiary axes (cymes)5; up to now we did not find development from from the apical meristem previously reported4.


Fig. 2: Flower diagram.
The flowers in the family Lauraceae are small, inconspicuous, greenish to cream colored, and radially symmetrical. The perianth consists of whorls of only slightly differentiated tepals (possibly a primitive condition)4.

 


Fig. 3: Flower before anthesis, perianth partially removed.
The flowers are bisexual4. The male floral organ, the stamens, occur in three to four trimerous whorls (Persea three), with the innermost whorl sterile and the third whorl having a pair of glands at the base. In Persea the nectaries are at the inner fertile whorl, and filaments are longer than the anthers. A characteristic feature of the family is the presence of flaps (Persea four) on the anthers, which open from the base upwards and pull out the pollen as they open4.

 


Fig. 4: Stamen, inner ferile whorl, from periphery, flaps, nectaries, sterile neighbors, hairy filament.
The female floral organ (gynoecium) is unicarpellate with a superior ovary containing one ovule with placenta arranged basally4. In Persea americana initiation of flowering begins in late July to October, followed by anthesis seven months later5.

 

 


Fig. 5: Young flower, perianth and stamen partially removed, single carpel with ascidiate base and plicate stylar-stigma portion.
Flowers can be protogynous, and protandrous in the same individual (details see below).
In the base of the receptacle, the stele gives off the median bundles of the tepals. The remaining vascular cylinder is rearranged to form two carpel bundles, the ventral bundle runs through the funiculus to the chalaza of the ovule, and the dorsal bundle extends to the stigma. The stamens arise from the traces of the tepal bundles, and the staminal glands are derived from their respective stamen bundle.

Flower development of the Lauraceae has been studied most recently by Boyle6.

 

  Vegetative Characters: Lauraceae are generally trees or shrubs, mainly evergreen, with alternate to opposite leaves which are simple, entire and coriaceous; stipules absent4; however, some are climbing parasites (Cassytha). The leaves often produce ethereal oils, a characteristic of the Magnoliales. The genus Persea has strictly alternate leaves.

Reproductive biology: Flowers of Persea (and a few other genera of Lauraceae) can be protogynous, meaning the stigma is receptive before the pollen is shed, and protandrous, meaning the pollen is shed before the stigma is receptive, in the same individual. This way, self-pollination (of the same flower) is avoided. However, flowers on an entire tree are in different stages, and self-pollination does occur occasionally, but the young fruits fall from the tree prematurely, alluding to a possible post-zygotic self-incompatible mechanism6. Pollination of the flowers is mainly by bees. Normally, taxonomic group are either proterandrous or proterogynous, to find both phenomena together on one individual, as in Persea, is unusual.


Fig. 6: Avocado: fruits of Persea americana.

Use: Other members of the family include Cinnamomum (cinnamon and camphor), Laurus (bay leaves and Greek laurel of antiquity), Sassafrass (food flavoring) and Cassytha (devil's tresses), a parasite with a flexible, string-like shoot, occuring in tropical and subtropical countries. Cinnamomum was once the most economically important of the family, but now Persea americana, the avocado, holds that title. It also produces an oil, estragol, in the leaves that is used in the cosmetics industry and also has insecticidal properties. The fruit has the highest energy content of any fruit and is high in its vitamin and mineral content, as well as a good source of mono-unsaturated fat, and soluble and insoluble fiber7. In poor areas of the New and Old World (where it is now widely cultivated), it has been coined the “poor man’s butter”.

Persea americana in the Floral Genome Project (FGP): The FGP studies genes in flower development of key taxa of the flowering plants (angiosperms)8,Tree of Life. Important questions in the evolution of the flower are, how genes evolved their diversity of sequences and paralogs, and their interaction. Persea represents a large family among the important group of basal flowering plants, Magnoliales, sometimes considered related to other important groups (such as monocots)9,10,11,12. Lauraceae have an fossil record as old as the cretaceous13,14. At the same time, Persea americana is ealily available because of its importance as crop plant. Availability of sufficient plant material is a necessity for the study of the expression of a multitude of genes.


Literature Cited

1) Renner, S.S., Chanderbali, A.S. 2000. What is the relationship among Hernandiaceae, Lauraceae, and Monimiaceae, and why is this question so difficult to answer? Int. J. Plant Sci. 161 (6 Suppl.): S109-S119.

2) Chanderbali, A.S, van der Werff, H., Renner, S.S. 2001. Phylogeny and historical biogeography of Lauraceae: Evidence from the chloroplast and nuclear genomes. Ann. Missouri Bot. Gard. 88: 104-134.

3) The Angiosperm Phylogeny Group II. Bot. J. Linn. Soc. in press.

4) Rohwer, J.G. 1993. The Families and Genera of Vascular Plants II. Lauraceae. Kubitzki, K., Rohwer, J.G., Bitrich, V. (eds.), Berlin : Springer-Verlag.

5) Salazar-Garcia, S., Lord, E.M., Lovatt, C.J. 1998. Inflorescence and flower development of the 'Hass' avocado (Persea americana Mill.) during "on" and "off" crop years. J. Am. Soc. Hort. Sci. 123(4): 537-544.

6) Boyle, E.M. 1980. Vascular anatomy of the flower, seed, and fruit of Lindera benzoin. Bull. Torreya Bot. Club. 107:409-417.

7) Bergh, B.O. 1995. Lauraceae. In: Smartt, J. & Simmonds, N.W. (eds.) Evolution of Crop Plants, 2nd Edition. London: Longman.

8) Soltis, D.E., Soltis, P.S., Albert, V.A., Oppenheimer, D.G, dePamphilis, C.W., Frohlich, M.W., Theißen, G. 2002. Missing links: The genetic arcitecture of the flower and floral diversification. Trends Plant Sci. 7: 22-31.

9) Qiu, Y.-L. Lee, J., Bernasconi-Quadroni, F., Soltis, D.E., Soltis, P.S., Zanis, M., Zimmer, E.A., Chen, Z. Savolainen, V. Chase, M.W. 2000. Phylogeny of basal angiosperms: analyses of five genes from three genomes. Int. J. Plant Sci. 161 (6 Suppl.): S3-S27.

10) Qiu, Y.-L. Lee, J., Whitlock, B.A., Bernasconi-Quadroni, F. Dombrovska, O. 2001. Was the ANITA rooting of the angiosperm phylogeny affected by Long-Branch Attraction? Mol. Biol. Evol. 18: 1745-1753.

11) Soltis, P.S. Soltis, D.E., Zanis,M.J. Kim, S. 2000. Basal lineages of angiosperms: Relationships and implications for floral evolution. Int. J. Plant Sci. 161 (6 Suppl.): S97-S107.

12) Soltis, D.E. Soltis, P.S., Chase, M.W., Mort, C.M., Albach, D.C., Zanis, M., Savolainen, V. Hahn, W.H., Hoot, S.B., Fay, M.F., Axtell, M., Swensen, S.M., Prince, L.M., Kress, W.J., Nixon, K.C. Farris, J.S. 2000. Angiosperm phylogeny inferred from a combined data set of 18S rDNA, rbcL, and atpB sequences. Bot. J. Linn. Soc. 133: 381-461.

13) Eklund, H. 2000. Lauraceous flowers from the Late Cretaceous of North Carolina, U.S.A. Bot. J. Linn. Soc. 132: 397-428.

14) Eklund, H., Kvacek, J. 1998. Lauraceous inflorescences and flowers from the Cenomanian of Bohemia (Czech Republic, Central Europe). Int. J. Plant Sci. 159: 668-686.


The Virtual Flower
The Floral Genome Project (FGP)

Soltis Lab

University of Florida


Matyas Buzgo, 08 Jan 2003