The Malva Pages
within section Bismalva
The hybrid between Malva alcea and Malva moschata is known as Malva ×intermedia Boreau . I have seen an apparently sterile plant, grown as Malva alcea 'Fastigiata', which otherwise favoured Malva alcea in appearance. This may have been Malva ×intermedia. Kristofferson  reproduced this cross experimentally. He found the hybrid to resemble Malva alcea in height. Its stems possess both simple (as in Malva moschata) and stellate (as in Malva alcea) hairs. The mericarps, when produced, are only hairy on the upper side, rather than generally, as in Malva moschata. (Malva alcea has glabrous mericarps.) The epicalyx is intermediate in form between those of the parent species. Malva ×intermedia was found to be highly sterile, as would be expected from its triploid nature.
I raised, in 2005, from a cross made in 2004, plants of parentage Malva alcea 'Fastigiata' × Malva moschata alba, and Malva alcea 'Fastigiata' × Malva moschata rosea. Seed production was easy, and germination of the seed good, but prolonged. The plants obtained have the general aspect of Malva alcea, but are completely sterile, and have a long flowering season. One plant was exinvolucellate. In the other plants the form of the epicalyx overlapped that of Malva alcea. This is probably a consequence of the seed parent possessing particularly broad bracteoles.
between sections Bismalva and Malva
The hybrid between Malva alcea and Malva sylvestris is known as Malva ×egarensis Cadevall ; that between Malva moschata and Malva sylvestris as Malva ×inodora Ponert. . The latter is recorded from Czechslovakia. (Flora Iberica  has Malva ×egarensis as Malva fastigiata × moschata, i.e. a synonym of Malva ×intermedia.)
These are wide crosses, and I have some skepticism as to whether they do occur. I have attempted to experimentally reproduce them, without success. A total of 15 crosses were attempted between the species pairs alcea × durieui, alcea × sylvestris, durieui × moschata, moschata × australiana, moschata × dendromorpha, moschata × linnaei, moschata × sylvestris, sylvestris × alcea and sylvestris × moschata.
Of these Malva durieui × Malva moschata alba produced quantities of apparently good seed, which germinated readily, but which on flowering turned out to be Malva durieui (it's difficult to reliably emasculate Malva durieui early enough to avoid self-pollination); Malva moschata alba × Malva sylvestris Hardwick s.n. produced 4 seeds; and Malva sylvestris 'Mystic Merlin' × Malva moschata alba produced fruits but no seeds. Neither germinated. The remaining crosses did not produce fruit.
Kristofferson  has also experimentally investigated crosses between these sections; he found that no seed was producted in the crosses moschata × sylvestris and moschata × neglecta, and the cross moschata × verticillata produced unfilled seed.
within section Malva
Extensive hybridisation is possible within this section.
The hybrid between Malva parviflora and Malva sylvestris is known as Malva ×arbosii Sennen; that between Malva neglecta and Malva pusilla as Malva ×henningii Goldbach , Malva ×adulterina Wallr.  or Malva ×hybrida Celak. ; that between Malva pusilla and Malva sylvestris as Malva ×littoralis Dethard ; that between Malva neglecta and Malva sylvestris as Malva ×zoernigii Fleischmann ; that between Malva nicaeensis and Malva sylvestris as Malva ×tetuanensis ; and that between Malva nicaeensis and Malva parviflora as Malva ×narbonensis Sennen .
Malva ×adulterina is recorded from Germany, Austria, Czechslovakia, Poland, Romania and the former Soviet Union. Malva ×zoernigii is recorded from France, Germany, Austria and Czechslovakia.
A single plant assigned to Malva neglecta × parviflora is recorded from southern England. This cross can be readily reproduced artificially, and the hybrids are highly fertile. They are intermediate between the parents in patterning of the dorsal faces of the mericarps, and in the nature of the angle between the dorsal and lateral faces. The fruiting pedicels combine the parental forms, the upper being very short, and the lower long and deflexed [3, 6]. Further experimental hybridisation by Kristofferson  reproduced Malva ×zoernigii and Malva ×henningii, and also produced the hybrid Malva parviflora × pusilla. All these hybrids, although they have reduced fertility, produce appreciable quantities of seed.
Kristofferson also successfully crossed Malva verticillata with Malva pusilla, Malva nelgecta and Malva sylvestris. These hybrids are all highly sterile. He was unable to cross Malva verticillata with Malva parviflora.
Malva ×decipiens Rouy is a synonym of Malva ×littoralis . Malva ×barcinonensis Sennen is a synonym of Malva ×arbosii Sennen 
between section Malva and Lavatera section Anthema
Hybrids are reported between Lavatera cretica (Malva linnaei) and Malva nicaeensis; between Lavatera cretica (Malva linnaei) and Malva sylvestris; and between Lavatera mauritanica (Malva durieui) and Malva sylvestris . I have reproduced the last two.
Malva sylvestris × Malva durieui
This cross was made in 2003, using Malva sylvestris 'Braveheart' as the seed parent, and a single plant was obtained from the resulting seed. The seed was germinated in late summer 2003, and the plant overwintered indoors. It came into flower in spring 2004 and flowered strongly until mid-summer, and continued to flower into the autumn. This plant is highly sterile; a total of 6 seeds were obtained from it in 2004, and about half of these have the appearance of being unfilled. The plant died in the early winter of 2004, although protected from frost. However 4 cuttings were successfully taken, and grew strongly (indoors) overwinter. After being placed outdoors in the spring these repeated the floral phenology of the original plant.
The cross was repeated in 2004, using 'Mystic Merlin', 'Zebrina' and Hinsley 3 as the seed parent, and the reverse cross made, using Hinsley 3 and Hardwick s.n. as the pollen parent. Seed set using Malva sylvestris was variable: Hinsley 3 × durieui had fruit set, but limited seed set (2 seeds from 4 fruits); 'Zebrina' × durieui has fair seed set (12 seeds from 2/3 fruits) and 'Mystic Merlin' × durieui nearly complete seed set. In all cases seed germinated, and on reaching flowering side was found to be hybrid. Both crosses with durieui as the seed parent had good seed set, but after the resulting seeds were germinated and grown to flowering size it was discovered that in all cases where Malva durieui was used as the seed parent prevention of self-pollination by emasculation of the flowers had been unsucessful, and the plants obtained were Malva durieui.
This hybrid produces small quantities of seed (seed set of less than 1%). Even at this low rate several hundred seeds were obtained in 2005 from the cuttings of the 2003 cross, but only a single seed germinated. With the exception of one plant, of uncertain nature, and higher fertility, only one other F2 seedling was obtained from seed collected from the other plants.
Malva sylvestris × Malva linnaei
This cross was made in 2003, using Malva sylvestris 'Braveheart' as the seed parent, and a single plant was obtained from the resulting seed. The seed was germinated in late summer 2003, and the plant overwintered indoors. It flowered in 2004, but not to any great extent.. This plant is highly sterile; no seeds were obtained from it in 2004. The plant has been overwintered (protected from the worse frosts). In 2005 it produced fruits, which developed considerably, but mostly abscissed before maturing. A few seeds were obtained.
The cross was repeated in 2004, using 'Zebrina' and Hinsley 3 and Hinsley 53 as the seed parent. Seed set using Malva sylvestris was good, and germination fair in the latter two cases. I await the plants reaching flowering size to confirm their hybrid nature. No germination was obtained of the cross Malva sylvestris 'Zebrina' × Malva linnaei.
Malva sylvestris × Malva australiana
This cross was made in 2004, with Malva sylvestris 'Mystic Merlin' as the seed parent and Malva australiana as the pollen parent. Fruit and seed set occurred and seed was germinated in 2005.. However the plants obtained from this seed were Malva sylvestris.
The reverse cross was also made in 2004, with Malva australiana as the seed parent, and Malva sylvestris Hinsley 3 as the pollen parent. Seed was obtained, and two seeds were germinated. Unfortunately one seedling was lost at the pricking out stage, due to a handling error. I await the other seedling reaching flowering size to confirm its hybrid nature.
within Lavatera section Anthema
Hybrids between Lavatera assurgentiflora (Malva assurgentiflora) and Lavatera venosa (Malva pacifica), perhaps also including Lavatera occidentalis in their parentage, are grown in gardens in California.
Hybrids between Lavatera arborea (Malva dendromorpha) and Lavatera plebeia (Malva australiana) are reported from Australia. 
I have attempted to reproduce this cross, without success. (The difference in flowering times of these two species means that opportunities to attempt this cross are sparse.)
within Lavatera section Olbia
The hybrid between Lavatera olbia and Lavatera thuringiaca is known as Lavatera ×clementii . Clonal cultivars belonging to this hybrid are extensively grown in gardens in temperate regions. The hybrid Lavatera olbia × triloba is also recorded .
I have raised backcrosses between Lavatera thuringiaca and Lavatera ×clementii. I have also raised backcrosses between Lavatera ×clementii and cultivars assigned to Lavatera olbia. However, I have not yet successfully hybridised Lavatera thuringiaca and Lavatera olbia.
between section Bibracteolae and section Malva
Malva ×turolensis Sennen is Malva stipulacea × sylvestris . (Malva stipulacea probably refers to Malva trifida.) This is a wide cross, and I am skeptical that it does in fact occur.
between section Bibracteolae and Althaea section Hirsutae
×Malvalthaea transcaucasica (Sosn.) Iljin is interpreted as a hybrid between Malva aegyptia and Althaea hirsuta.
other named hybrids
Malva ×duri Sennen is Malva liabulifolia x sylvestris (M. liabulifolia is probably a synonym of some other Malva species); Malva ×hybridica Pau & Vicioso is Malva loeflingiana × stipulacea.  (Malva stipulacea probably refers to Malva trifida. Malva liabulifolia and Malva loeflingiana are probably synonyms of some other Malva species.)
The Malva Pages
If you have found any errors on this page, or have any further information about hybrids in the genera Malva, Althaea (section Hirsutae) and Lavatera then please contact me at firstname.lastname@example.org.
© 2004, 2005, 2006, 2008, 2009 Stewart Robert Hinsley