Germination of Cistus ladanifer seeds in relation to parent material

Plant Ecology 133: 57–62, 1997. 57c 1997 Kluwer Academic Publishers. Printed in Belgium.

Germination of Cistus ladanifer seeds in relation to parent material

Felix Perez-GarcıaDepartamento de Biologıa Vegetal, Escuela Universitaria de Ingenieria Tecnica Agrıcola, UniversidadPolitecnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain

Received 23 October 1996; accepted in revised form 4 July 1997

Key words: Cistaceae, Hard-coated seeds, Heat pretreatment, lntraspecific variability, Rockrose, Seed storage

Abstract

Variability in seed germination behaviour of Cistus ladanifer L. (rockrose), a Cistaceous species widely distributedin the Mediterranean Basin, was studied in a central Spanish population under controlled conditions. No correlationbetween seed moisture content and germination was found. Great variability in germination was found amongseeds of the population studied, not only between seeds belonging to different mother plants, but also betweenthose collected from different capsules on the same plant. In most cases, seeds preheated at 100 �C for 30 minutesshowed a significant increase in germination. This germination behaviour is related to fire regimes as this plantis a typical shrubby element of the mediterranean shrublands. Percent germination did not vary significantly afterseveral months of seed storage at room temperature. In the same way, no difference was found in final germinationpercentage of seeds stored under room temperature vs. seeds stored under cold conditions.

Introduction

The genus Cistus L. (Cistaceae) comprises over 16shrubby species with a circummediterranean distri-bution. In that area it forms a significant part of thevegetation. Cistus species are not exclusively depend-ent on fire for their regeneration. Therefore, they mustnot be considered as typical pyrophytes, but as plantsoccupying highly disturbed sites (e.g., burned areas),abandoned agricultural lands or perturbed woodlands(Trabaud 1995). Cistus species multiply naturally byseed and they possess an opportunistic strategy of seedgermination (Thanos & Georghiou 1988; Thanos et al.1992; Trabaud 1995).

Cistus ladanifer L. (rockrose) is a very commonwestern Mediterranean shrub, This species occurs onpoor soils, growing in dry, sunny places within a rangefrom the S of France and the Iberian Peninsula (Spainand Portugal) to N Morocco and Algeria (Talavera et al.1993). It does not spread by clonal growth. This spe-cies behaves as coloniser on highly degraded areas.Hardness and impermeability to water of the seed coatmight be the most important causes of the dormancypresent in this species (Corral et al. 1989; Corral

et al. 1990; Valbuena et al. 1992), since they occurin several other species of the genus Cistus (Thanos &Georghiou 1988; Trabaud & Oustric 1989a,b; Corralet al. 1990; Thanos et al. 1992; Valbuena et al. 1992).The positive effect of heat pretreatments on seed ger-mination of Cistus species has been investigated byseveral authors (Vuillemin & Bulard 1981; Troumbis& Trabaud 1986; Thanos & Georghiou 1988; Trabaud& Oustric 1989a,b; Corral et al. 1990; Roy & Sonie1992; Valbuena et al. 1992; Perez-Garcia 1995; Tra-baud 1995). The dry-heat pretreatment is one of themost effective methods increasing germination in theseeds of C. ladanifer (Corral et al. 1990; Valbuenaet al. 1992). The massive recolonization observed onburned sites by C. ladanifer seedlings probably followthe breakage of seed dormancy through high temper-atures, similar to the situation noted for several otherCistus species (Trabaud & Oustric 1989a).

Cistus seed populations have been regarded aspossessing considerable heterogeneity in germinationbehaviour (Vuillemin & Bulard 1981; Thanos &Georghiou 1988). In such populations, only a smallsoft-coated fraction of seeds (usually less than 25%)can germinate each year, while the larger fraction

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of hard-coated and water-impermeable seeds accumu-lates in the soil seed bank (Thanos & Georghiou 1988).The softening of those seeds can be promoted, undernatural conditions, by heat generated by fire (Thanoset al. 1992). In undisturbed sites, the soft-coated seedfraction assures the maintenance of existing Cistuspopulations (Thanos & Georghiou 1988). In each Cis-tus population, it is possible that this soft-coated seedportion belongs to a small number of maternal plants.

In the present work, we studied intraspecific dif-ferences in the germination behaviour of C. ladaniferseeds and attempted to relate germination performanceto the site of origin of the seed in the mother plant. Thespecific objectives of this work were as follows: (1)to study the effect of the mother plant on seed ger-mination; (2) to test the possible correlation betweenseed moisture content and germination and possibleeffects between heated pretreatments and germinationpercentages; (3) to study seed germination over timeafter seed storage under different conditions.

Material and methods

Plant material and seed storage

Dry fruits (capsules) containing mature seeds ofC. ladanifer were collected from a unique homogen-eous population near the town of Soto del Real, Mad-rid province (Central Spain, 40 �450 N 3 �470 W). Thepopulation studied was surveyed regularly from thebeginning of the summer in 1994 to determine theoptimum date to collect the capsules. All capsules werecollected on 27 July 1994. The criterion followed toselect the capsules was that they were completely ripe.The seeds from all selected capsules, likewise, showeda similar degree of ripeness, as was observed fromtheir colour and hardness. At the time of collection ofcapsules, seeds were completely developed. Germina-tion experiments were carried out with seeds belongingto: (1) ten capsules randomly collected from just onemother plant chosen at random (Table 1); (2) a uniquecapsule randomly obtained from each of ten differ-ent mother plants randomly chosen (Table 2); (3) tencapsules randomly harvested from ten different moth-er plants chosen at random (Table 3). Only in thislast experiment, for each mother plant the seeds fromdifferent capsules were bulked. The number of seedscollected per capsule ranged between 469 and 1,118(x = 728:38� 39:84; N = 20).

Table 1. Effect of heat pretreatment at 100 �C for 30 minutes onthe germination of Cistus ladanifer seeds belonging to 10 capsulesfrom just one mother plant. Mean values in a column followed bythe same letter are not significantly different at the 5% level ofprobability as determined by the least significant difference test.Each value is the mean of 4 replicates of 25 seeds each.

Final germination percentages � standard error Relative Sa

increase in

Untreated seeds Preheated seeds germinationb

5 � 0.7 a 90 � 0.0 b 17.00 �

6 � 0.0 a 90 � 2.8 b 14.00 �

7 � 0.7 ab 93 � 2.1 b 12.29 �

9 � 0.7 ab 84 � 0.0 ab 8.33 �

8 � 2.8 ab 73 � 3.5 a 8.12 �

11 � 0.7 b 87 � 4.9 b 6.91 �

12 � 2.8 b 82 � 7.1 ab 5.83 �

14 � 0.0 b 74 � 4.2 a 4.29 �

18 � 0.0 b 82 � 0.0 ab 3.56 �

47 � 4.9 c 92 � 2.8 b 0.96 �

a S significance of untreated-preheated differences; �p < 0:05.b Relative increase in germination compared with the untreatedseeds.

Table 2. Effect of heat pretreatment at 100 �C for 30 minutes on thegermination of Cistus ladanifer seeds belonging to 10 capsules from10 mother plants. Mean values in a column followed by the sameletter are not significantly different at the 5% level of probabilityas determined by the least significant difference test. Each value isthe mean of 4 replicates of 25 seeds each.


increase in


6 � 1.4 a 80 � 0.0 ab 12.33 �

15 � 4.9 b 87 � 2.1 b 4.80 �

16 � 1.4 b 86 � 5.7 b 4.37 �

18 � 0.0 bc 87 � 0.7 b 3.83 �

21 � 3.5 bc 83 � 0.7 ab 2.95 �

29 � 0.7 cd 78 � 5.7 ab 1.69 �

40 � 1.4 d 84 � 0.0 ab 1.10 �

40 � 1.4 d 83 � 3.5 ab 1.07 �

57 � 0.7 e 76 � 4.2 ab 0.33 ns

64 � 0.0 e 73 � 7.1 a 0.14 ns

a S significance of untreated-preheated differences; �p < 0:05; ns,non significant.b Relative increase in germination compared with the untreatedseeds.

The seeds were kept in hermetic glass contain-ers and stored in the laboratory at room temperature(approximately 20 �C). The duration of storage of theseeds before the trials was at least eight months. Tostudy the effect of storage conditions on seed germin-

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Table 3. Effect of heat pretreatment at 100 �C for 30 minutes onthe germination of Cistus ladanifer seeds from 10 different motherplants. Mean values in a column followed by the same letter arenot significantly different at the 5% level probability as determinedby the least significant difference test. Each value is the mean of 4replicates of 25 seeds each.


increase in


12 � 1.4 a 75 � 3.5 ab 5.25 �

14 � 2.8 a 62 � 2.8 a 3.43 �

20 � 2.8 ab 78 � 2.8 bc 2.90 �

19 � 0.7 a 74 � 1.4 ab 2.89 �

21 � 2.1 ab 75 � 0.7 ab 2.57 �

30 � 7.1 bc 90 � 0.0 d 2.00 �

32 � 2.8 bc 70 � 2.8 ab 1.19 �

37 � 7.8 c 70 � 4.2 ab 0.89 �

38 � 2.8 c 68 � 2.8 ab 0.79 �

77 � 3.5 d 87 � 3.5 cd 0.13 ns

a S significance of untreated-preheated differences; �p < 0:05; ns,non significant.b Relative increase in germination compared with the untreatedseeds.

ation, a fraction of seeds was stored at room temperat-ure for 4 months and subsequently in a cold chamberat 5 �C, while another fraction was always stored in acold chamber at 5 �C. These trials were carried out withseeds belonging to ten different mother plants chosenat random. For each mother plant the seeds from tencapsules randomly collected were bulked (Tables 4 &5).

Seed weight and moisture content

For each mother plant, the average weight of threereplicates of one hundred seeds each was scored. Seedmoisture content was determined gravimetrically bydrying seeds in an oven at 130 �C for 2 hours. Two orthree replicates of 100 seeds each were used accordingto seed availability.

Seed germination tests

The seeds were tested for germination on top of twofilter paper discs (Whatman #1), previously moistenedwith 3 ml of distilled water, in 7-cm diameter glass Petridishes. Each dish contained 25 seeds, evenly spaced,and there were four replicate dishes for each trial. Thedishes were placed in a germination chamber at con-stant temperature of 15 �C under a 16-h light photoperi-

Table 4. Final germination percentages (mean values � stand-ard error) of Cistus ladanifer seeds from 10 different motherplants as influenced by storage time at room temperature. Com-parisons are made among storage times for each mother plant.Mean values in a row followed by the same letter are not sig-nificantly different at the 5% of probability as determined bythe least significant difference test. Each value is the mean of 4replicates of 25 seeds each.

Storage time (months)

8 14 21

30 � 7.1 a 37 � 2.6 a 32 � 7.5 a

38 � 2.8 a 36 � 1.4 a 42 � 4.1 a

20 � 2.8 a 24 � 3.7 a 23 � 3.8 a

37 � 7.8 a 32 � 2.4 a 28 � 3.2 a

32 � 2.8 a 41 � 5.9 a 36 � 1.4 a

14 � 2.8 a 12 � 4.5 a 11 � 2.6 a

19 � 0.7 a 14 � 5.4 a 29 � 3.5 a

12 � 1.4 a 8 � 2.0 a 13 � 2.6 a

77 � 3.5 a 67 � 5.0 a 64 � 9.5 a

21 � 2.1 a 15 � 5.6 a 11 � 2.2 a

od and an irradiance of 35 �mol m�2 s�1 provided bycool white fluorescent tubes. This incubation temperat-ure was chosen because the relatively low temperaturesare the most suitable for the germination of variousCistus species (Vuillemin & Bulard 1981; Thanos &Georghiou 1988; Corral et al. 1990). This germinationbehaviour is a typical strategy of mediterranean plants(Thanos et al. 1992; Thanos & Doussi 1995; Thanoset al. 1995). The filter papers were kept moist, and ger-minating seeds were counted and removed every threedays for a 42-day incubation period. The criterion ofgermination was emergence of a radicle through theseed coat.

Dry-heat pretreatment

The dry seeds, spread on glass dishes, were placed inan oven already at 100 �C for 30 minutes and then 100seeds (four replicates of 25 seeds each) were incubatedat constant temperature of 15 �C under a 16-h lightphotoperiod. A previous report (Corral et al. 1990)showed that a thermal shock of 30 minutes at 100 �Cresulted in optimal germination of C. ladanifer seeds.

Statistical analysis

For each trial, the final germination percentages werecalculated and arc-sine transformed values were sub-jected to analysis of variance. A comparison of means

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was carried out through the least significant differencetest (LSD) at the 5% level of probability.

Results

Seed weight and moisture content

The mean weight of one hundred seeds (� standarderror) varied from 20.0 mg (�0:5) to 24.5 mg (�0:2),depending on the mother plant considered. The differ-ences in weight per 100 seeds between plants were notfound to be significantly different. Seed moisture con-tent, expressed as percentage of fresh weight, rangedbetween 6.2% and 7.9% for different mother plants. Inthe population studied, no significant relationship wasfound in any case between germination and the seedmoisture content.

Variability in germination behaviour

Table 1 shows the germination percentages reached byseeds belonging to ten capsules from just one motherplant after 42 days at 15 �C. Significant differences inthe germination percentages of untreated seeds werefound, ranging from 5% to 47%. On the other hand, theheat treatment at 100 �C for 30 minutes, just before theseeds were sown, significantly increased germinationin all cases. In the same way, significant differences inthe germination percentages of preheated seeds werefound (Table 1). The relative increase in germination,compared with the untreated seeds, ranged from 0.96to 17.00 (Table 1).

Table 2 shows the germination percentages reachedby seeds belonging to individual capsules from tenmother plants. Germination percentages of untreatedseeds ranged between 6% and 64%, depending onthe capsule. As in the previous test, heat pretreatmentsignificantly increased germination for most capsules.As before, the germination percentages of preheatedseeds were found to be significantly different (Table 2).The relative increase in germination, compared withthe untreated seeds, ranged between 0.14 and 12.33(Table 2).

The above results indicate that there is consider-able variability in germination behaviour within thepopulation studied, not only between seeds belongingto different mother plants (Table 2), but also betweenthose obtained from the same plant (Table 1).

Table 3 shows the germination percentages after42 days at 15 �C for ten different mother plants of

Table 5. Final germination percentages (mean values � standarderror) of Cistus ladanifer seeds as influenced by storage durationunder different storage conditions. Seeds stored at room temperaturefor 8, 14, and 21 months (A); seeds stored at room temperature for 4months and subsequently for 4, 10, and 17 months in a cold chamberat 5 �C (B); seeds stored in a cold chamber at 5 �C for 8, 14, and 21months (C). The seeds belonging to 10 different mother plants werebulked before separation into the different treatments. Comparisonsare made among storage conditions. Mean values in a row followedby the same letter are not significantly different at the 5% level ofprobability as determined by the least significant difference test. Eachvalue is the mean of 4 replicates of 25 seeds each.

Storage time Treatment Storage conditions

(months) A B C

8 Untreated seeds 29 � 0.7 a 33 � 0.7 a 37 � 3.5 a

Preheated seeds 62 � 1.4 a 82 � 7.1 a 60 � 5.7 a

Sa � � ns



Sa � � �



Sa � � �

a S, for each storage treatment, significance of untreated-preheateddifferences; �p < 0:05; ns, non significant.

the population studied. Germination percentages ofuntreated seeds ranged from 14% to 77% dependingon the mother plant, which shows the high intraspe-cific variability in germination behaviour that can befound in C. ladanifer. In the same way, significant dif-ferences in the germination percentages of preheatedseeds were found, ranging from 62% to 90% (Table 3).In most cases, seeds pretreated with dry heat showeda significant increase of the final germination percent-age. The relative increase in germination, comparedwith the untreated seeds, ranged between 0.13 and5.25 (Table 3).

Seed storage conditions and germination

Table 4 shows the germination percentages reachedby seeds originating from ten different mother plantsstored at room temperature for 8, 14, and 21 months.For each mother plant the seeds from ten capsules har-vested were bulked. Both, capsules and plants wererandomly chosen. As can be seen, for seeds from everymother plant, percent germination did not vary signi-ficantly with time of storage at room temperature.

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Table 5 shows the germination percentages reachedby seeds stored under different conditions for 8, 14,and 21 months. In this experiment, the seeds belong-ing to ten different mother plants were bulked. Thetransformed germination percentages were not foundto be significantly different between the storage con-ditions assayed. In the same way, no significant differ-ence in ability to germinate was detected among thedifferent times of storage. However, heat pretreatmentimproved significantly the germination, compared withthe untreated seeds, in most cases studied.

Discussion

It has been established that germination of someseeds is influenced by environmental and physiologicalfactors operating during ripening of seeds on the moth-er plant (Grant Lipp & Ballard 1963; Evenari et al.1966; Datta et al. 1972; Gutterman 1978, 1980/81,1992, 1993, 1994a,b,c; Bewley & Black 1994; Kigel1995). The results obtained in the present study indic-ate that the seeds of C. ladanifer in the populationstudied are characterized by considerable heterogen-eity in their germination behaviour (Tables 1–5). Thisresult is not uncommon and has been observed in seedsof several species (Cavers & Harper 1966; Neuffer &Hurka 1988; Perez-Garcıa 1993; Gutterman 1980/81,1994a,b,c; Francisco-Ortega et al. 1994; Kigel 1995;Perez-Garcıa et al. 1995). The production of seeds withdifferent germinability is one of the most important sur-vival strategies for species growing under unpredict-able environmental conditions (Gutterman 1994a,b,c;Kigel 1995). Seeds from different mother plants with-in the population studied displayed very variable finalgermination percentages (Tables 2 & 3). Even withinone mother plant, seeds belonging to different cap-sules showed a considerable variability in germina-tion (Table 1). Variation in dormancy and germinationamong the seeds within a plant has been observed invarious species (Gutterman 1992, 1994c; Perez-Garcıa1993; Bewley & Black 1994; Francisco-Ortega et al.1994).

The ability to produce seeds with different degreesof dormancy is, most probably, a mechanism by whichC. ladanifer, as other species (Gutterman 1994a,b,c;Kigel 1995), adapts to new environmental situationsand ensures its survival by facilitating the germinationof its seeds over time.

The dry-heat pretreatment of C. ladanifer seedsincreased their germination significantly (Tables 1, 2,

3, & 5). High temperatures are supposed to promotethe cracking of the seed coat, particularly the palisadelayer of macrosclereid with its strongly lignified cellwalls (Corral et al. 1989), simulating the promotingeffect of fire. The results obtained are very similarto those reached by seeds from other populations ofC. ladanifer (Corral et al. 1990; Valbuena et al. 1992),and support the conclusion that, as occurs similarlyin several other plants of fire-prone regions (Parker &Kelly 1989), this species has a strong heat resistance.In addition, the massive recolonization observed onburned areas by C. ladanifer seedlings can be due tothe break of seed dormancy through high temperaturesduring a fire.

The results obtained show that the seeds ofC. ladanifer live longer than one year. Seeds storedin the laboratory at room temperature for differentperiods (8, 14, and 21 months) reached very similargermination percentages (Table 4). As in other specieswith opportunistic strategies of germination (Gutter-man 1994a,b), C. ladanifer produces a great numberof long-lived tiny seeds per plant. A long-lived seedbank is very important for species inhabiting areas withunpredictable amounts and distribution of rain (Gut-terman, 1994a,c). It is well known that seed longevityis associated with hardness and impermeability of theseed coat (Rolston 1978; Baker 1989; Bell et al. 1993).On the other hand, there were no significant differencesin germination percentages between seeds stored under‘warm’ (room temperature) vs ‘cold’ conditions (5 �C).

The above results make clear the decisive import-ance of seed origin in the germinability of C. ladanifer.The origin of the seeds should always be taken intoaccount in order to define models of germination beha-viour, specially in wild species, given their morpholo-gical and physiological variability. The variability ofthe germinative response between seeds of one speciesis a relatively frequent fact in wild plants, which shouldbe always considered when trying to extrapolate to awhole species data obtained from a genotypically lim-ited material. Furthermore, knowledge of seed age aswell as seed storage conditions is essential in interpret-ing the results obtained in seed germination studies.

Acknowledgements

I thank Eufemia Aparicio for her assistance in thefield and three anonymous referees for their valuablecomments and corrections on an earlier version of themanuscript.

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Germination of Cistus ladanifer seeds in relation to parent material

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