Nuclear DNA Amounts in Pteridophytes

Annals of Botany 87: 335±345, 2001 doi:10.1006/anbo.2000.1339, available online at http://www.idealibrary.com on Nuclear DNA Amounts in Pteridophytes M I C H A E L D . B E N N E T T * and I L I A J . L E I TC H Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, UK Received: 9 October 2000 Accepted: 13 November 2000 Published electronically: 26 January 2001 DNA amounts (C-value and genome size) are much-used biodiversity characters. A workshop held at Kew in 1997 identi®ed major gaps in our knowledge of plant DNA amounts, recommending targets for new work to ®ll them. Murray reviewed non-angiosperm plants noting that representation of pteridophyte species (approx. 0.42 %) was poor, while locating C-value data for them was very dicult. The workshop con®rmed the need to make data for other groups besides angiosperms accessible for reference purposes. This paper pools DNA C-values for 48 pteridophyte species from eight original sources into one reference source, and ful®ls a key workshop recommendation for this group. Comparing these data shows that nuclear 1C-values in pteridophytes vary approx. 1000fold, from 0.055 pg in Selaginella species to about 55 pg in Ophioglossum petiolatum. Genome size estimates for 25 pteridophytes vary approx. 200-fold from 0.055 to 10.7 pg, and the mean genome sizes in diploids and polyploids (5.15 and 4.59 pg, respectively) are not signi®cantly di€erent. Wider comparisons show that ranges of genome sizes in the major groups of land plants are very di€erent. Those in bryophytes and pteridophytes are narrow compared with those in gymnosperms and angiosperms. The data indicate that the origin of land plants possibly involved a ®rst major increase in genome size in the evolution of vascular plants, while a second such increase occurred later in gymnosperms. C-values for pteridophytes remain very few, but conversely opportunities for new work on them are # 2001 Annals of Botany Company many. Key words: Pteridophyte DNA amounts, DNA C-values, nuclear genome sizes. I N T RO D U C T I O N Nuclear DNA C-value and genome size are important biodiversity characters with fundamental biological signi®cance and many uses (Bennett and Leitch, 1995; Bennett et al., 2000). Collected lists of C-values for angiosperms have been published as reference sources since 1976 (Bennett and Smith, 1976, 1991; Bennett et al., 1982; Bennett and Leitch, 1995, 1997). These were pooled in a list with C-values for 2802 species from 306 original sources, and a ®rst version of the Angiosperm DNA C-values database (Bennett et al., 1997) was published electronically in April 1997. Given the broad and growing demand for information on plant DNA C-values, it is clearly important to monitor what is known, and to recognize what is unknown and needed most (Bennett, 1998). A workshop and discussion meeting focussing on these issues was held at the Royal Botanic Gardens, Kew (RBG, Kew) in September 1997, sponsored by the Annals of Botany. This was attended by 86 scientists from 15 countries with expertise in generating, or interest in using, information on plant nuclear DNA amounts. Papers from the discussion meeting were published as a special issue entitled `Genome size in plants' in Annals of Botany (volume 82, Supplement A) (see Bennett and Leitch, 1998). The workshop's recommendations were reported orally to participants at the meeting, and a summary is available on the web [see: http : //www.rbgkew.org.uk/cval/conference.html (under Angiosperm Genome Size Discussion Meeting)]. A key aim of the 1997 workshop was to identify major gaps in our knowledge of plant DNA C-values and to * For correspondence. Fax ‡44 (0)20 8332 5310, e-mail m.bennett@ rbgkew.org.uk 0305-7364/01/030335+11 $35.00/00 recommend targets and priorities for new work to ®ll them by international collaboration. Presentations on regional ¯oras, and analysis of representation of data in the Angiosperm DNA C-values database all highlighted huge gaps in our knowledge, both in terms of the low numbers of species represented, but also in terms of systematic, life form, ecological and geographic representation. For example, no C-value estimate was available for approx. 68 % of angiosperm families. At the workshop Murray reviewed our knowledge of Cvalues in non-angiosperm plants. Representation was much better for gymnosperms than for angiosperms, as values were published for about 16 % of gymnosperm species (Murray, 1998) compared with about 1 % of angiosperms. However, the situation was worse for pteridophytes (approx. 0.42 %), and almost no C-value data were available for bryophytes (approx. 0.1 %), although locating C-value data for these two groups had proved very dicult. The workshop concluded that this level of ignorance was unacceptable. New targeted work was essential to improve representation of both angiosperms and the other less known plant groups. Diculties encountered in locating Cvalue data for review at the workshop clearly demonstrated the value of user-friendly reference works. Thus, there was a clear need to bring together DNA amount data for species in groups other than angiosperms, and make them easily accessible in one plant C-values database. Two key targets were agreed for angiosperms, namely to obtain (1) a ®rst C-value for 2500 (approx. 1 %) species, carefully targeted to give improved geographical, life form, ecological and systematic representation, including (2) at least one C-value estimate for all families. Bennett et al. # 2001 Annals of Botany Company 336 Bennett and LeitchÐNuclear DNA Amounts in Pteridophytes (2000) and Hanson et al. (2001) noted signi®cant progress towards achieving these two goals and emphasized the importance of targeting, which seems essential to reach the goals set by the 1997 workshop within 5 years. Bennett et al. (2000) also reviewed progress towards achieving recommendations for several non-angiosperm groups. No time-bound targets were set at the 1997 workshop for estimating numbers of species' C-values in such groups. Perhaps in consequence, new C-values for gymnosperms or pteridophytes published since 1997 have remained rare, although a signi®cant advance in systematic coverage has occurred for bryophytes. Prior to 1997, there were published estimates for only about 18 bryophyte species (Reski et al., 1994; Renzaglia et al., 1995), but since then, estimates for a further 34 species have been published by Zouhair and Lecocq (1998), Lamparter et al. (1998) and Temsch et al. (1998, 1999); Voglmayr (2000) estimated Cvalues for 138 moss taxa in 34 families in a carefully targeted benchmark study whose main aim was to cover a representative spectrum of moss taxa. Thus, the need to combine the scattered C-value data for bryophytes into one reference list is now greatly increased. Soon after the 1997 workshop, a collected list of C-values for 117 gymnosperm species from 24 original sources was published, making them available in a sing (...truncated)