Algae

While algae comprise a polyphyletic assemblage of organisms, collated data on genome size for any of these was not available until 2004 when release 3.0 of the Plant DNA C-values database included C-values for Chlorophyta, Rhodophyta and Phaeophyta for the first time. The main bulk of the data comes from work by Kapraun (2005) who assessed knowledge of C-values in these algal groups and concluded that species representation was poor (Table 7.1). Kapraun also highlighted that (i) an absence of data for Micromonadophyceae (an algal group con sidered to be ancestral to Chlorophyta, Rhodophyta, Phaeophyta, and all land plants), and (ii) very limited data for the charophycean lineage of Chlorophyta (the group considered sister to all land plants) should be addressed. Consequently, targets for increasing data in these groups have now been set.

The Extent of Genome Size Variation across Plant Taxa

Given the available data, it is clear that there is considerable variation in the genome size profiles between plant groups as shown in Fig. 7.2. Angiosperms are by far most variable with C-values ranging nearly 2000-fold from 0.065 pg in the carnivorous plant Genlisea margaretae (Lentibulariaceae; Greilhuber et al. 2005, 2006) to over 125 pg in tetraploid Fritillaria assyriaca (Liliaceae). Currently the least variable group is the Phaeophyta (brown algae) where reported C-values range just nine-fold from 0.1 to 0.9 pg. However, as discussed above, species representation for all but gymnosperms is poor, thus the range and distribution of C-values reported may not be entirely representative and may increase as new data are obtained. For example, the known range for bryophytes recently increased substantially from just 12-fold (based on 176 species' C-values) to 73-fold following the report of (i) 1C = 0.085 pg for the hornwort Anthoceros agrestis, An-thocerotaceae (this is less than half the size of the bryophyte with the previously smallest C-value of 0.2 pg), and (ii) 1C = 6.42 pg for the liverwort Mylia taylorii, Jungermanniaceae (three times larger than the previously largest bryophyte with

Angiosperms •

- 6.3(0.06-127.4)

Gymnosperms •

17.0 (2.3-32.2)

Monilophytes •

13.6 (0.8-72.7)

Lycophytes

3.8 (0.2-12.0)

Bryophytes

0.5 (0.09-6.4)

Chlorophyta •—

1.8 (0.1-19.6)

Phaeophyta •

0.4 (0.1-0.9)

Rhodophyta •

0.4 (0.1-1.4)

0 25 50 75 100 125 150 1C DNA amount (pg)

0 25 50 75 100 125 150 1C DNA amount (pg)

Fig. 7.2 Range of C-values in plant groups shown as a line with the mean 1C-value as a dot. The figures give the mean C-value in picograms followed by the minimum and maximum values in parentheses. Data for 4428 species taken from the Plant DNA C-values database (Bennett and Leitch 2005c; Greilhuber et al. 2006).

2.1 pg). Even angiosperms, which are most studied from a C-value perspective, can throw up surprises. A 1000-fold range for angiosperms was first reported in 1982 based on C-values for 993 species (Bennett et al. 1982). This range remained the same for the next 24 years. However, in 2005 the report that a carnivorous plant Genlisea margaretae has a lC-value of only 0.065 pg (Greilhuber et al. 2005) has nearly doubled the range of known C-values in angiosperms (0.065-127.4 pg).

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