Genetic Resources and Crop Evolution 47: 335–343, 2000.
Genetic relationships among Hibiscus syriacus, Hibiscus sinosyriacus and Hibiscus paramutabilis revealed by AFLP, morphology and ploidy analysis
J.M. Van Huylenbroeck, J. De Riek & M. De Loose

Abstract: The genetic relationships between and within Hibiscus syriacus, Hibiscus sinosyriacus and Hibiscus paramutabilis, three winter hardy Hibiscus species native to China, were analysed by the amplified fragment length polymorphisms (AFLP) technique and by morphological evaluation of flower and leaf characteristics. Both methods clearly discriminated between the three species. H. sinosyriacus was classified as an intermediate form between H. paramutabilis and H. syriacus; however, it showed a higher similarity to H. paramutabilis. The different H. syriacus cultivars could be identified by AFLP analysis, while also leaf indices clustered the different cultivars in small groups. Flow cytometry showed that both triploid and tetraploid cultivars occur in the H. syriacus assortment. In general triploid cultivars had larger flowers compared to diploid cultivars.

Figure 1. Schematic overview of the measured Hibiscus leaf parameters.

Leaf indices

To measure the different leaf parameters, fully developed leaves (located between fifth and 10th internode of newly formed shoots) were collected in August from three different plants of each cultivar. From each leaf an image was taken by a colour camera (JVC, KY-F55B, Japan) connected to a frame grabber (Flashbus, Integral Technology, US). Calculations on the images were done using the software WIT version 5.2 (Logical Vision, US). The following indices were determined (Figure 1): leaf length over width (L/B), angle of leaf basis (a), relative width of the mid lobe (M/B), relative length of the side lobes (C/L) and relative depth of indentation of the lobes (A/L).

Morphological characteristics

H. syriacus cultivars are frequently classified by their flower characteristics: flower colour and flower type (single, semi-double or double). Single flowers are larger than semi-double or double ones (Table 1). Flower diameters presented in Table 1 are in general 1-1.5 cm smaller than those reported by Van de Laar (1997). However, in the latter study only the largest flowers during a warm blooming season were measured, while our data are averages of two subsequent growing years and of different flowers during the complete blooming period. H. paramutabilis and the H. sinosyriacus cultivars all have large, single flowers (Table 1).

An overview of the different leaf indices measured in this study is given in Table 2. Indices giving a relative measure were preferred to absolute values, e.g., leaf length and width, because they are supposed to be independent from leaf size or developmental stage. Species could be easily discriminated by the indices leaf length over width (L/B) and angle of the leaf base (α). L/B and were strongly correlated (correlation coefficient, -0.851). Both H. sinosyriacus and H. paramutabilis had a significantly lower L/B ratio and a greater leaf angle compared to H. syriacus (Table 2). Compared to H. paramutabilis, H. sinosyriacus had a smaller leaf angle and a lower M/B ratio (Table 2). H. sinosyriacus showed a leaf form intermediate between the two other species. This is in agreement with Bates (1965) who also considered H. sinosyriacus as an intermediate form based on morphological data of leaf shape.

Within H. sinosyriacus, ‘Lilac Queen’ had the greatest leaf angle, while ‘Melmauve’ could be distinguished from ‘Autumn Surprise’ and ‘Ruby Glow’ by a higher L/B and also a lower absolute leaf length and width (data not shown). ‘Autumn Surprise’ and‘Ruby Glow’ differed in the forms of the side lobes as expressed by the C/L and A/L ratio (Table 2). Within H. syriacus the leaf indices L/B, and M/B were valuable to distinguish different cultivars from each other (Table 2). The values for ‘Helene’, ‘Diana’, ‘Purple CV2’ and ‘Red Heart CV’ were comparable with those published earlier by Shim et al. (1993).

In Figure 2 an ordination based on the morphological data of the leaves is presented. A clear separation between species was obtained. Only ‘Purpureus Variegatus’ and ‘Diana’ were clustered together with the H. sinosyriacus cultivars instead of with the H. syriacus accessions. Identification of different cultivars based on their leaf morphology is possible only to a certain degree. In some cases additional information (plant habit, growth vigour, flower characteristics) is needed for exact identification.

Hibiscus syriacus biblio