This is how he tells about himself:

From my school years I have been interested in cacti, in the last years I also took up gardening. My collection of cacti is rather old and peculiar. It has been influenced by many factors but only two of them are really of importance.

• Firstly, I have a wide range of interests for the plants. Any rational considerations are somehow pushed into the background. I could begin growing plants obviously not suitable for my dwelling conditions, e.g. Hilocerii, or to accumulate a strange collection of Selenicerii, or to make Cereus peruvianus bloom and so on.
• Secondly, I'm awfully conservative. I hate to part with plants once they came into my possession. If I lose a species I make every effort to fill the empty space with a plant of the same species, even if it is not rare or valuable. I hardly ever change my plants for more showy or decorative. There are exceptions though: I feel no remorse parting with plants with a proven taxonomical discrepancy.

Photo 2. Plants from the genus Rhipsalis from D.Semenov's collection

To my pity I don't know exactly how many plants and species there are in my collection. Some years ago I began to make a computer database of my collection. Now there are about 800 entries in it and I think this is only a half.

I specialize in cacti belonging to the genus Rebutia and epiphytic cacti. It's easy to account for the first of them – a Rebutia was one of the first cacti to enter my house. As to the epiphytic cacti I was strongly influenced by S. Volgin, who had been writing a thesis and shared with me some information on Rhipsalis and also his considerations on its evolutionary relations.

Besides these groups I have a special interest in Parodia (including Notocactus), Echinopsis (including Lobivia), Frailea, Echinocereus, Mammillaria and Opuntia.

Photo 3. A group of Rebutias from D.Semenov's collection.

In winter I keep my plants in the glassed-in loggia of my Moscow apartment, in summer I move them to the country cottage. I'm extremely pressed for time and lack strength to give my plants thorough care. During many years that I grow cacti there have been times when I lost interest in them. These periods coincide with my most serious losses – not so much of cacti as of information on them.

Photo 4. Winter-hard Opuntia cultivar "Andreas Sokolov" which bloomed in outdoor garden of D.Semenov in 2003.

Since the middle of 1975 I took part in activities of the Moscow club of cacti fans. In the eighties I was rather an active member of the club, later also of the All-Russian association.

I appreciate perhaps three things in cacti.
1). Cacti are marvelous. They are infinitely beautiful and tremendously interesting to watch and contemplate. When I compare them with other cultivated plants I never tire out to wonder at their numerous benefits.
2). Cacti is an almost ideal object for collecting. An urge to collect is inherent to almost everybody and collecting cacti is a part of a man's attitude to the world, a distinct and reliable component of his life strategy.
3). I love to converse with fellow cacti fans – in person, by mail, through publications. There are so many interesting people who give the real joy of communication!

Beginning with the seventies I have published a lot of popular and special articles on cacti and other succulents in various periodicals of Russia and Germany.

I consider them not as a serious contribution to cactology but as a normal way of communication. I'm also the author of several popular books. There I think I owe some explanation. To publish a book is traditionally considered here as a certain achievement. Nevertheless it is only a fulfillment of a certain order of the publishers. Such books as a rule only to a small extent reflect the real merits of their author. However I don't lose hope to publish the author's version of the book on cacti, and now I'm working on it.

All my people take my hobby patiently and help me when they can. My son is a student and lives separately. He won't grow cacti, of that I'm sure.