The Evolution Of Flowering Time Biology Essay

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Herbarium is a repository, a facility designed to ensure long-term preservation of scientific plant samples, generally referred to as specimen Horton (2003). The University of Reading United Kingdom has up to 300,000 plant species in their herbarium that can be used for in the study of flowering time and their changes, undergraduate studies and other research. Herbarium specimens are also very important because they can be used for different purposes such as identification of plant species, genetic data, and historical distribution of plant species. Herbarium specimens are collected for scientific analysis. Specimen collected are laid out on newspaper so they can be pressed and dried with the aid of plant dryer or with blotters and ventilators so that water can be totally extracted from the specimens. The dried specimens are the transferred onto a sheet were polyester or a thread is used to hold the specimens firmly together on the sheet. Specimens with seeds and fruits are placed in are packet which are later attached onto the sheet. A label containing all the information of the specimen is then created, the information includes; the Latin and common name of the plant, the location it was collected from/herbarium name, date, country, county or state, latitude and longitude, altitude, habitat, plant formation, collectors name etc. The label containing this information is then attached to the lower right hand corner of the sheet. The aim of the label with the information on is to enable easy identification/knowing more details about the collected specimen by other collectors. Herbarium specimens are then store according to species group or taxonomy in a paper folder which then divided into their various genus and family in different folders before they are finally kept in their various cabinets and entered in herbarium database (a computer programme used to store information or data collected from the herbarium) herbarium data are stored in database for ease of access to information on a particular specimen or species. However there are factors that can affect the survival of herbarium specimen and these are insect control, archival materials and specimen restoration. Most insects found in herbarium are attracted to dried plants while others accompany specimens brought from other locations. Insects found in herbarium are controlled by chemicals called naphthalene or paradichlorobenzene which are placed in the storage compartment with the specimens. Specimen restoration can be carried out by restoring herbarium specimen that has not been properly mounted on the sheets.


Data from herbarium specimens shows whether a particular specimen is flowering or not on the date it was collected. Herbarium specimens are also made up of long term phonological data on different types of brought from various places species around the world Fitter et al., (1995). Apart from collecting data from herbarium specimens, photograph from a plant specimen have been used to estimate the peak of flowering time in plant species. Information gotten from a photographed herbarium specimen can also be used in studying the changes in response to climate change Fitter et al.,(1995). Photographic data from herbarium specimens contain information of different phonological event occurring in the plant such as leaf-out, bird migration and spring emergence of other organisms. Information also gotten from photograph and herbarium data are used to study long term trends in phonological events and how they relate to climate change. Studies carried out shows that herbarium specimens has a strong correlation among flowering dates which indicates that plants flowered in the same order every year in most plant species Miller-Rushing et al., (2006). Herbarium data in the past have been used to study the responses in plant flowering time to changing spring temperature over the past century and this has showed that plants flower earlier due to warmer spring temperature Primack et al., (2004). They have also in the past been used in studying the flowering times of fleshy and non-fleshy fruits. Bolmgren et al (2005) carried out a study with herbarium data collected from the Swedish Natural History Museum to study flowering time in fleshy and non- fleshy fruited plants species. A total of 5500 specimens were used for the study, the specimens used were collected over the period of 1813 to 2000. The herbarium data were made up of recorded dates from all the flowering specimens. For each species, the mean flowering date was recorded, the mean flowering date based on 90% of the specimens, that is 5% tails of early and late opening tails were not included and the first flowering date derived by taking the collection date of the first flowering specimen after excluding the first flowering 10% were all recorded Bolmgren et al (2005). They also evaluated the flowering time date from the herbarium specimen by comparing the correlation between flowering times from 26 species collected from two field data sets and the herbarium data set. Analysis were also carried out in order to distinguish the differences between flowering time data collected from the herbarium and flowering time data collected in the field and to know if they were affected by the number of specimens collected from the herbarium that were used for the study per species of flowering season. From their study the discovered that in the north temperate provinces of Uppland and Sodermaland south-eastern Sweden showed that flowering times occur earlier in fleshy fruits taxonomy than in non-fleshy fruits due to the constraining effects of north temperate climate on phonology evolution. Their experiment also showed that the evolution flowering phonologies are affected by the ecological dispersal.


Flowering time is the period in which plants produce flowers which in most cases later develop into fruits and seeds. Most flowering time have life cycles while others have a period of vernalization before flowering. Exogenous and Endogenous are some factors that control flowering time in various species of plants, also some environmental signals such as light, temperature and photoperiod also contribute to the control of flowering time .light is detected by photoreceptor which are divided into three groups and these are- the phytochromes which detect red/far-red light, cryptochromes which detect blue/UV-A wavelength and the phototropin which also detects blue region spectrum. Phytochromes and cryptochromes are very important genes that occur in flowering time. PhyA promotes flowering under long day length and they play a big role in the opposition of flora transition, while PhyB delays flora transition by regulating genes in the photoperiod pathway. Most plants flower earlier because of warmer temperature in the spring. Plants control their flowering time just to make sure that they reproduce under favourable conditions. The time to which plant species flower is determined by both genetic and environmental factors, and by their interaction Fitter et al., (1995).There are certain factors that determine the flowering time of plant species and these are; climatic condition, temperature, day length. The control of flowering time is an important part of how plant adapt to their environment and a key trait incorporated in crop plant breeding programme.


Various pathways in the regulation of flowering time.


Photoperiod pathway

There are about seven 7 genes involved in the photoperiod pathway and these are GI, FT, FD, CO, FWA, FHA and FE. CO plays a major role in photoperiodic control of Arabidopsis Putterill et al (1995). GI mutant are low in CO mRNA which causes a late flowering stage in plants, however when excess CO is released, GI is then able to overcome late flowering.

Vernalisation pathway

Vernalisation pathway or response is very important in flowering time because of its effect on temperature. The ability for plants of different species to adjust or adapt to different weather conditions such as cold winter increases their chances of survival and flowering.

Gibberellins synthesis and signalling

Gibberellins is known for its promotion in plant growth in terms of flowering in long day plants, and its regulating power in plant growth. Studies have shown that the addition of exogenous gibberellic acid increases flowering in Arabidopsis under short day. Gibberellin plays a major role in stopping some proteins which are known as DELLA proteins.


Rapid changes in the flowering time of many British plant species has provided the biological evidence of recent climate change and inter-species differences which is likely to impact on the structure of plant communities and ecosystem Gordon Simpson(Anon). Climate change over the years has contributed to changes in seasonal activities of plants. Frank et al., (2007) study on Brassica rapa showed that climate change has affected the ecological dynamics of many plant species and it is also likely to impose natural selection on ecologically important traits , the result from their experiment also showed that a quick and adaptive evolutionary shift in flowering phonology after a climatic fluctuation. Plants that flower in response to photoperiod are classified as short day, long day and day neutral plants. Day length is a key factor in flowering induction many plant species in a seasonal environment with flowering induction usually happening at shorter day lengths in lower latitudes Dijk et al., (2006). Increase in temperature over the years has affected the length of growing season thereby disrupting the timing of leaf flush and leaf fall. Climate change is one of the major factors that have contributed to decrease in the length of growing period. Seasonal duration of leafing, flowering and fruiting determine phonological behaviour in tropical tree Singh et al.,(2006). Tropical trees have short flowering period at a specific time of the year which occurs at a particular phase of leafing phonology. Singh et al., (2006) showed that there is a reproductive survival strategy in the diversity of seasonal flowering time and fruiting duration, with linkages to leafing and leafless duration in tropical deciduous forest tree species. Global climate change is believed to be the cause of differences in timing duration and the changes found in phonological events found in tropical trees.


Different plant species respond to different photoperiods, for rice has a shorter photoperiod which makes it flower earlier when the photoperiod is shorter than the day length. Also plants like Arabidopsis thaliana and wheat are long day plants and they flower earlier when the photoperiod is longer than the day length .Latitudinal cline in some plant species is controlled by a flowering time gene known as FRIGIDA. Examples of these plants are Arabidopsis thaliana and Wheat. Wheat has a prolonged exposure to low temperature which in turn promotes its flowering in autumn sown variety that requires vernalization.A study carried out by Stinchcombe et al.,(2004) showed that flowering accessions has a positive genetic correlation between water use efficiency and flowering time in Arabidopsis and the effects of FRI of increasing effect of water use efficiency in accessions across different latitudes. Day length and cold winter are some of the main environmental signals that most plant uses so as to flower during the spring Putterill et al.,(2004). Day neutral plants are adapted to higher latitudes, they are found close to the equator which has a little change in its day length throughout the year. These plants rely on autonomous signal for flora initiation e.g. kidney bean Anon(2010).Autonomous signals are genes found in autonomous pathway and they include LD, FCA, FY, FPA, FVE FLD and FLK. Each of these genes has lead to a mutation increase in the levels of FLC mRNA and FLC proteins.


The aim of the project is to study the changes in flowering time of a British flora known as Cynara. The study is to be focused on a set of species from the British Isles. Data will be collected from the University of Reading herbarium. These results or data collected will compared with other data collected from other surveyors from previous years in order to study the correlation in their life history and trends of the specimens.



Cynara plant is a native to the Mediterranean. Cynara are thistle like perennials they possess ring of hairs on their shaft beneath the style branches from the family of Asteraceae which is the sunflower family, from the tribe of Cardueae. The evolution cynara is still unclear to evolutionary biologist and plant biologist; however there are ten known species of cynara and these are. Cynara algarbiensis, Cynara auranitica, Cynara baetica, Cynara cardunculus, Cynara cornigera, Cynara cyrenaica, Cynara humilis, Cynara hystrix, Cynara scolymus and Cynara syriaca. Cynara cardunculus is also known as Cardoon or Artichoke. It is mostly used for the manufacture of Southern European cheeses. Cynara humilis is a wild thistle that is traditionally used as a food by the Berbers. Cynara humilis is a native to Southern Europe and North Africa (Gardening Daily).

Hypothesis to be tested are;

Herbarium data can be used in the studies of flowering time

The latitude at which a Cynara is found is a determinant of flowering time.

Does day length affect flowering time in Cynara?

Does data from herbarium specimen show trends in flowering time?

Flowering time is determined by the species of plant and its taxonomic group.


Anon, 2010. Plant biology. Photoperiod response, photoperiodism. Viewed on 8th June 2010.

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Fitter, A.H., Fitter, R.S.R., Harris, I.T.B., & Williamson, M.H., 1995. Relationship between first flowering dates and temperature in the flora of a locality in Central England. British Ecological Society, 9, 55-58.

Franks, S.J., Sim, S., & Weis, A.E., 2007. Rapid evolution of flowering time by an annual plant in response to a climate fluctuation. Department of Ecology and Evolutionary Biology, University of California, 104 (4), 1278-1282.

Horton, D., 2003. University of Iowa Herbarium. Herbaria and specimens: what are they? Viewed on 10th June 2010.

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Primack, D et al., 2004. Herbarium specimens demonstrate earlier flowering times in response to warming in Boston. American Journal of Botany, 91 (8), 1260-1263.

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Singh, K.P., & Kushwaha, C.P., 2006. Diversity of flowering and fruiting phonology of trees in a tropical deciduous forest in India. Annals of Botany, 97, 265-272.

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